Parallel grinding method has been widely used for advanced optics machining, especially f-θ optics. In order to reduce the dependence on high-precision machine tool with many degrees of freedom (DOF) and obtain high machining accuracy, in this paper, we propose a simultaneous 2-axis method to replace the conventional simultaneous 3-axis method in parallel grinding. Firstly, the algorithm of the simultaneous 2-axis method is explained. Then, the motion control errors and machining errors under simultaneous 3-axis and 2-axis methods are comparably analyzed, respectively. Finally, through grinding experiments, the feasibility of the simultaneous 2-axis method is verified.