Abstract: To optimize the geometric accuracy and improve the forward design level of the five-axis horizontal machining center, a precision allocation method based on a genetic algorithm is proposed. A precision five-axis horizontal machining center produced by a company is selected as the research object. Firstly, its structure and error elements are analyzed, and the geometric error model is established by using the theory of multi-body system and the principle of homogeneous coordinate transformation. Secondly, the sensitivity of 37 errors in the error model is analyzed at different positions in the machining space, and the maximum sensitivity of a single error at each position is selected as the global sensitivity. Finally, based on the error model and sensitivity calculation results, Isight and Matlab software are combined to minimize the total cost and maximize the sum of the product of global sensitivity and error, and genetic algorithm is used for precision allocation. The results show that the machining center with precision allocation can reduce costs by 5.89% while maintaining the original precision, providing a theoretical basis for the process design of the five-axis machining center.