The numerical simulation of the detonation of a high explosive (HE) is difficult for traditional grid based methods due to the mesh distortion. Smoothed particle hydrodynamics (SPH) method,as a Lagrangian particle method,is a best candidate method to solve this kind of problem. Modified SPH method presented by the authors with fully variable smoothing length corrects the variable smoothing length effects of standard SPH method in essence,and improves the simulation precision and stability in the large density gradient problem. 1D TNT slab detonation and 3D TNT shaped charge were simulated with the new method and compared with the standard SPH method and theoretical value. The results show that the new SPH method improves the precision and computes the CJ value more correctly. With the numerical simulation for detonation process of the 3D TNT shaped charge,the properties and the rule of the gaseous detonation products were obtained. The results accord with the explosion theoretical value.