A new type of PRPaR-2CPR parallel robot mechanism with parallelogram branch chain was proposed.The mechanism was composed of one PRPaR branch chain and two CPRs.It had the characteristics of simple structure,low coupling and high stiffness.The topological design theory and method of parallel mechanism based on the POC equation were used to analyze and calculate the degree of freedom and kinematic properties.Kinematic equations were established using the constraint conditions of link length,and the inverse solution expression was obtained through calculation.At the same time,the positive numerical solution was obtained.In addition,according to the calculation and analysis,the existence conditions of singularity were obtained.Through the inverse solution expression of position,the limit boundary search method was used to obtain the performance maps of workspace and motion dexteri ty respectively,and the corresponding performance maps were drawn for analysis.Finally,it was expected to obtain better motion flexibility performance in the limited operating space.With the global dexterity in the task workspace as the optimization goal,genetic optimization algorithm (GA) was selected to optimize the structural parameters.The dexterity performance in the optimized task workspace has been greatly improved,so the motion performance of this kind of parallel mechanism is improved.