A novel terminal guidance law based on stochastic fast smooth second-order sliding modes control theory was proposed to handle the track imprecision mainly caused by stochastic maneuvering of the target, inertial lag, and model uncertainties. It is assumed that the target acceleration term was a zero mean Gaussian white noise and the missile-interceptor guidance system became a stochastic uncertain nonlinear system driven by additive noise, which did not have any equilibrium. So a concept of finite-time second-order mean-square practical convergence was presented and the finite-time convergence property of proposed control was proved. Then the direct hit sliding mode manifold was chosen and the guidance law was designed. The applicability of the new guidance law was illustrated through simulations of a guided missile intercepting a stochastic maneuvering target in tail chase and headon intercepts case, respectively. Results show the validity and effectiveness of the proposed method, while a comparison is made with the augmented proportional navigation guidance law, the traditional sliding mode guidance law and smooth second order sliding mode guidance law.