A spatial parallel robot mechanism with three translations and one rotation was designed.The degree of freedom and orientation feature set of the mechanism were analyzed by using the theory of orientation feature set.The inverse kinematics equation was derived according to the vector product and vector method,the forward kinematics solution of the mechanism was calculated by using Newton-Raphson method,and a group of numerical solution was selected to verify each other.The Jacobian matrix of kinematics was calculated and the singularity of kinematics was analyzed.The reachable workspace and fixed attitude workspace of the mechanism were analyzed,and the influences of parameters on the volume of workspace were analyzed.The mathematical optimization model of workspace volume maximization was established,and the whale optimization algorithm was used to complete the optimization design of parameters.The results show that the larger the L2 and r are,the larger the operating space of the mechanism is,and the larger the parameter value L1 and R are,the smaller the operating space range of the mechanism is;the optimal values of R ,r, L1, L2 are 1 mm,0.999 2 mm,0.3 mm and 1.5 mm respectively.