<p>The tolerance allocation of five-axis machine tools (FAMTs) significantly impacts production costs and product quality. Traditional tolerance allocation methods are frequently influenced by subjective factors and fail to focus on the impact of tolerance coupling effects. Therefore, a tolerance optimization allocation method for FAMTs considering tolerance coupling effects is proposed. First, a mapping relationship between the tolerances of key components and the resulting geometric errors is established following the topology of the FAMT. A volumetric error model is developed. Next, a new tolerance optimization allocation model is introduced. The model computes the weights of tolerance parameters in terms of the influence on volumetric error under coupled conditions and integrates a manufacturing cost model. The Non-dominated Sorting Genetic Algorithm (NSGA) is employed to address the optimization problem. The simulation and experimental results indicate that the average pass rate of the volumetric error distribution points reaches 95.29%, manufacturing costs are expected to decrease by 14.69%, and the average machining accuracy of the standard workpieces has improved by 19.20%.</p>