1. A folding bed structure, comprising a plurality of mounting sleeves, and an armrest assembly arranged between adjacent mounting sleeves, wherein the armrest assembly comprises: a joint connector, wherein the joint connector is symmetrically provided with two first sliding grooves near an upper part of the joint connector, and a distance between the two first sliding grooves gradually increases from top to bottom; and a second sliding groove is provided on each of sides, facing away from each other, of the two first sliding grooves;

two upper enclosing rods, wherein the two upper enclosing rods are located on both sides of the joint connector respectively, a first guide pin is provided at each of ends, adjacent to each other, of the two upper enclosing rods, and the first guide pin is embedded in the first sliding groove and is allowed to slide along the first sliding groove; a rod body part of the upper enclosing rod is slidably connected to the joint connector, a second guide pin is arranged on a rod body of the upper enclosing rod, and the second guide pin is slidably embedded in the second sliding groove;

when the folding bed structure is unfolded, the first guide pin is positioned on a top of the first sliding groove, and the second guide pin is positioned on an end, adjacent to the first sliding groove, of the second sliding groove; and when the folding bed structure is folded, the first guide pin slides to a bottom of the first sliding groove, and the second guide pin slides towards an end away from the first sliding groove;

two lower enclosing rods, wherein the two lower enclosing rods are respectively arranged under one upper enclosing rod side by side; and ends, away from each other, of the two lower enclosing rods are respectively rotatably connected to the mounting sleeves, and ends, adjacent to each other, of the two lower enclosing rods respectively carry a third guide pin that is embedded in and slides along a respective third sliding groove formed in a lower part of the joint connector, third sliding grooves extending up and down symmetrically; and when the folding bed structure is unfolded, each third guide pin is positioned at a bottom of a corresponding third sliding groove, and when the folding bed structure is folded, each third guide pin slides towards a top of the corresponding third sliding groove; and

a lower part of each of the plurality of mounting sleeves is connected to a support seat through an upright rod, and each support seat is hinged to an unlocking base arranged in a middle of a lower part of a bed body through a connection rod group, wherein the unlocking base comprises an upper unlocking base and a lower unlocking base that are inserted up and down; the connection rod group comprises an upper connection rod and a lower connection rod group that are arranged side by side up and down; both ends of the upper connection rod are respectively hinged to a side of the upper unlocking base and the support seat; and the lower connection rod group comprises a first lower connection rod and a second lower connection rod that are hinged; and an outer end of the first lower connection rod is hinged to the support seat, and an inner end of the second lower connection rod is hinged to the lower unlocking base; wherein, when the bed frame is folded, the upper unlocking base is configured to be held and lifted upward so that the upper unlocking base and the lower unlocking base are separated and simultaneously move upward, thereby simultaneously driving one end of the connected upper connection rod and one end of the lower connection rod group to swing upward, and the other ends of the upper connection rod and the lower connection rod group pull the plurality of support seats simultaneously to approach and gather towards the unlocking base, the support seats at four corners respectively driving the lower parts of the upright rods to retract inward to start a folding action; and, as the lower part of each upright rod retracts inward while a length of the lower enclosing rod remains constant, an upper part of each upright rod expands outward and pulls the upper enclosing rod to move outward through the mounting sleeve, whereby the upper enclosing rod drives the first guide pin to gradually move outward and downward along the first sliding groove and the joint connector gradually falls; and when the upper unlocking base is lifted to a highest position, the first guide pin is at the bottom of the first sliding groove and the joint connector is lowered to a lowest position.