An adjustable bed includes: a head frame assembly; a foot frame assembly; a knockdown connecting bracket; a slidable assembly having a pair of slidable assembly sides slidable within a pair of lower C steel brackets in a slidable assembly upward direction or a slidable assembly downward direction; a plurality of slidable assembly angle steels; a pair of head lift arm bracket assemblies; a second head tilt angle bracket; a head tilt platform; a head lift platform; a lumbar lift bracket assembly; an upper seat platform; a support platform; a lower seat platform; a head lift motor, secured to the head frame assembly for driving the pair of head lift arm bracket assemblies in a head lift forward direction or a head lift backward direction; and a head support tube, having an upper end pivotally connected to a L bracket and a lower end connected to the head lift platform.