From the theory of instantaneous expansion of detonation product and momentum conservation,  this paper obtains velocity calculation model of explosively formed projectile (EFP) and the model is revised due to the influence of the ratio of charge altitude to charge diameter.  This paper calculates the velocities of EFPs formed by large apex angle liner and sphere liner through the velocity calculation model and the results are consistent with the numerical simulation and experiment results.  This velocity calculation model is applicable in engineering.