A knockdown bed is formed of a first bed frame and a second bed frame. The first bed frame includes a top side, a bottom side, and an insertion member. The insertion member has an insertion end, a fixed end connected with the bottom side, two lateral sides, and two abutment surfaces connected with the two lateral sides. The two abutment surfaces gradually approach each other from the fixed end to the insertion end. The second bed frame includes a top side, a bottom side, and a slot member adjacent to the first bed frame. The slot member is formed of two sidewalls, two abutment walls connected with the two sidewalls, and a slot, into which the insertion member can be inserted to interconnect the first and second bed frames. In this way, the knockdown bed can be easily assembled and structurally firm.