Considering the fact that large deviatoric deformations are always localized in a small narrow region in hypervelocity impact problems,a method named subdomain computation for SPH(smoothed particle hydrodynamics) is developed.The entire computational domain is divided into several subdomains.In subdomains where large deformation is developed more particles are placed,and in subdomains where only small deformation is developed fewer particles are placed.Computational instability induced at interface of two subdomains is discussed and a method to handle the instability is proposed.Numerical simulations of a rod projectile penetrating into a thick target are carried out with the method and traditional SPH.It shows that computation accuracy as well as computation efficiency are improved.