The invention discloses a porous ceramic 3D printer and forming method. The 3D printer comprises a frame-shaped machine frame, wherein a lifting platform is arranged in the frame, lifting mechanisms of a lead screw nut transmission structures are arranged on the two sides of the frame, rollers are arranged at the front end and the rear end of the machine frame, the front end roller is immersed inan adhesive box, a laser generator and a controller are arranged at the top end of the machine frame, and a laser cutting mechanism capable of cutting at any positions is further arranged at the top of the machine frame. According to the 3D printer and the method, synchronous servo motors, synchronous belts and the like are arranged at the front, rear, left and right parts so as to ensure the precise movement and positioning of the front-rear-left-right directions of a laser head, the cutting is accurately carried out, a first reflector and a second reflector adopt a two-time 45-degree refraction mode, laser emitted by a horizontal laser is refracted into the laser head, the moving laser head and the fixed laser are always in space vertical, a residual material recycling structure is connected with a residual material recycling rod by adopting the synchronous servo motors, accurate and continuous feeding is guaranteed, and porous ceramic with complex shape can be prepared convenientlyand quickly through a modified technology.