Abstract: In this article, the relation between the rate of solidification of metal under pressure and working velocity of punch during liquid forging have been studied experimentally and analyzed theoretically. The Coordinate equation of liquid metal forging process is first given. Solidification theory of metal has been related with plastic formation theory. This equation points out theoretically the rule of the working velocity of equipment and the demand for it in liquid metal forging. This is important to the practice of liquid metal forging technology.