Introduced the structural characteristics of a 3D-print pen based on the principles of Pistons continuous working ,and then established the mathematical model of the system. Compared with the other 3D-print pen, its print materials changed into liquid material ,such as liquid chocolate, from ABS plastic. The 3D-print pen had the advantages of reasonable design, convenient operation, and extended print material range. These were benefit for development and design of the other 3D-print pen.