At the early stage of product design, the information about mould, blank and boundary condition are not definite. It is difficult to calculate with incremental method. For solving this problem, one-step finite element method(FEM) was put forward in recent years. It starts from product shape, takes it as the middle plane of formed part, disperses it and determines the location of nodes in initial blank at certain boundary conditions with finite element method. Then the corresponding blank shape can be obtained by one-step FEM. In this paper it is discussed that the basic theory of one-step FEM and the research of the key technology. And it is simulated the pressing of auto panel with one-step FEM. It is put forward that the final part should consider the effect of the technology. Through comparing one-step FEM with incremental method, it is showed that one-step FEM could calculate rapidly and had some credibility. It was suitable to evaluate the formability at the early stage of product design.