A precision synthesis method of manipulator mechanism based on the optimal precision model is proposed. The genetic algorithm is used to optimize the tolerance allocation of D-H parameters, which provides a theoretical basis for the precision design of the manipulator. Taking a 7DOF cooperative manipulator based on the dualmotor servo drive joint as the research object, the geometric positioning accuracy of the manipulator is designed to be 1. 4 mm. The geometric positioning error model of the end-effector of the manipulator is established. The sensitivity analysis of parameter errors is implemented to find out the parameter errors which have a relatively great influence on the geometric position errors of the end-effector of the manipulator. According to the optimal precision mathematical model, the genetic algorithm is used to optimize the tolerance allocation of D-H parameters. After error simulation calculation and analysis, the maximum geometric positioning error of the manipulator is 1. 226 7 mm, with an average value of 0. 485 9 mm and variance of 0. 216 5 mm. This result meets the design requirements and provides a theoretical reference for the manufacturing and assembly of the manipulator. Compared with the precision synthesis method based on the minimum cost model, the precision synthesis method proposed in this paper does not need statistical manufacturing cost information and can ensure that the design precision of the manipulator meets the design requirements. It can be used for the precision design of single or small-batch manufacturing manipulators.