Abstract: For the problem of detonation driving plate, if some quantities could be gained from theories or experiments, we can deduce the projection angle formula from the projection angle equation. Using the equation, regarding the projection angle as a small quantity, neglecting the differentiation of the absolute value of the tangential velocity with respect to the time, the P.C.Chou formula was easily obtained. When considering the differentiation of the absolute value of the tangential velocity with respect to the time, the improved P.C.Chou formula was obtained. Compared to the P.C.Chou formula and Taylor formula, the results from the improved formula are more close to the experiment.