By the study object of 4-DOF 2-RPC/2-SPC parallel mechanism, the forward solution equation of the mechanism was listed. Through analyzing the coupling relationships among the position and orientation variables of the moving platform, geometric constraint equations were obtained. By combining the equations as auxiliary and the forward solution equation, finally through the reduction, an eighth order equation about q was obtained, and all of the forward solutions for position of mechanism were solved. This method makes the non linear forward equations easier and simple with fast solution speed. Moreover a specific example is introduced to verify the validity of method.