For high precision machining of asymmetric boring holes, a control technology of the Giant Magnetostictive Actuator (GMA) used in a precision high-load pinhole boring device was explored. According to the hysteresis nonlinearity of the GMA, the mathematic mechanism of the quasi static modified Prandtl-Ishlinskii(P-I) model was analyzed briefly. To broaden the application frequency domain and to improve the precision of quasi static modified P-I model，a modified dynamic P-I model was proposed by combining with hysteresis phase feedforword compensation, and good control results were obtained. The experiment of back loop control system based on the dynamic modified P-I model and a PID controller was conducted. Results after compensation show that the hysteresis nonlinearity of GMA has reduced from 14.5 %-67.2 % to 1.5%- 4.3% at the case of open loop control, which controls the nonlinear error of the hysteresis . Moreover, a boring experiment for an oval pin hole was performed, the obtained ovality accords with the requirement of drawings, and verifies the feasibility of the proposed method. The research in this paper provides a new method for machining high-load oval pinholes.