The important factors to affect the limit speed of a projected plate driven by explosive are first analysed in this paper. This analysis is combined with a discussion about the range of application of the empirical formulae. Then two important laws，which are summarized from the results of the numerical computations to two-dimensional projected plate，are formulated: ①When mass ratios of explosive and projected plate are the same，there is a certainly similar relation among limit speeds of two-dimensional projected plate；② The revised Gurney Formula may be used to calculate the limit speed of two-dimensional projected plate.