A state feedback H_infty optimal disturbance attenuation for model reference control of rigid robotic systems is studied. Disturbances affecting system dynamics come from residue of applied torques due to perturbation of system parameters and external noise. Disturbance attentuation level must be less than or equal to desired positive value gamma. By combining nonlinear minimax control technique with the work of Johansson (1990) we are able to present an explicit global solution to this nonlinear time-varying H_infty control problem. In particular, it turns out that if gamma, the desired attenuation level, is greater than the magnitude of the weighting matrix on control inputs, then a state feedback law achieving the desired performance can be explicitly constructed. Extensive simulations are made for tracking control of a two-link robotic manipulator with proposed H_infty design. reference: [1]Chen B S, Lee T S, Feng J H. A nonlinear H∞ control design in robotic systems under parameter perturbation and external disturbance[J].International Journal of Control, 1994, 59(2): 439-461. [2] Johansson R. Quadratic optimization of motion coordination and control[C]//1990 American Control Conference. IEEE, 1990: 836-841. link: https://shi.buaa.edu.cn/liujinkun/zh_CN/jxzy/8049/list/index.htm