To bear more loads for heavy truck pistons, the shape of heavy truck piston pinhole is often designed as non-cylinder form. Current methods cannot meet the needs for precision machining on non-cylinder piston pinhole (NCPPH). A novel mechanism based on giant magnetostrictive materials (GMM) is presented. New models are established for the servo mechanism, GMM, and magnetizing force of the control solenoid to characterize the relationship between the control current of the solenoid and the displacement of the giant magnetostrictive actuator (GMA). Experiments show that the novel mechanism can meet the needs to perform fine machining on NCPPH effectively.