Abstract: The H∞ problem of nonlinear control systems is studied in the sense of viscocity solution. The motivation on the study of viscocity solution of nonlinear H∞ control with the saddle point condition is due to the difficulty in the analysis of smooth solutions in some cases. The method is based on the game theory and Hamilton-Jacobi-Issacs (HJI) inequality. The main results are composed of three parts. The solution of HJI inequality of disturbance attenuation has been extended to the case without any assumption of smoothness. A control law in the light of the viscocity optimal solution is given, with a proof of the system stabilization when external disturbance vanishes. At last, some analyses on approximate algorithms are proposed for the nonlinear H∞ problems and a draft approxiamte polynomial algorithm is described.