The utility model relates to a bed with changeable size, which comprises a bed box, wherein a side shaft on a long edge of the bed box is connected with a bed board; the height of the bed board is equal to that of the bed box; two vertical grooves with same width are formed at the upper end and the lower end on one side facing to the bed box; bottom edge shafts of the grooves are connected with supporting legs; the height of the supporting legs is equal to that of the bed box; and the supporting legs can be placed in the grooves. When the bed is used and the area of the bed box needs to be enlarged, the bed board is put up and the supporting legs are put out from the grooves to level the bed board and the bed box so that the area of the bed can be increased. The bed with changeable size has the advantages of simple structure, convenience and practicability, reasonable construction and the like, and effectively solves the problems that the prior bed has fixed area and is inconvenient for people to use.