The model of position can be acquired and solved based on symbolic method concerning a three degree of freedom (3DOF) 3SPS3SRR parallel mechanism. Firstly, set up static and dynamic coordinate systems, the constraint equations were established for the mechanism through matrix transformation. The closedform expression of constraint equations of posture of the mechanism would be gotten by Sylvester elimination method to obtain single variable input output equation of the mechanism, in next. At last, by solving practical examples, 32 sets of real number solution were obtained for the mechanism in ordinary posture, and the mechanism was positioned in a special posture, then its closed form expression was compared with predicted one so as to verify the correctness of position solution model. In general, the model of position analysis of the mechanism based on symbolic method that is correct, efficient in characters and shortcomings avoidance of numerical method, has important significance and practical valve to analysis of the 3SPS3SRR parallel mechanism.