Taking cylindrical hole shaft joint surface as the research object, the actual error model of hole shaft joint surface with coupled tolerance was studied based on the new generation of GPS standard system. Taking cylindricity for instance, combining with the cylindrical form error evaluation method in the GPS standard, the external associated size actual change interval solving model of the cylindrical hole shaft surface was established, and the effect of actual error on fitting property was analyzed by using Monte Carlo method to simulate the random error. The formation mechanism of hole shaft joint surface error under the coupling effect of three kinds of tolerance, including direction tolerance and position tolerance, was analyzed, the actual error models of cylindrical hole shaft joint surface under different fitting properties were established, and the actual change interval of each error component of the joint surface and actual fitting property were obtained. Hole shaft actual assembly accuracy prediction in the design phase was achieved by taking the tolerance optimization design of the hole and shaft parts with the actual hole shaft joint surface accuracy and fitting property requirements as the constraints, and hole shaft processing cost as the objective. Finally, the feasibility and practicability of this method were verified with an example of hole shaft assembly accuracy analysis and tolerance optimization.