The parameter adjustment of the washout algorithm greatly affects its performance. To address the shortcomings of the current classical washout algorithm when it is applied to flight simulators, an improved washout algorithm based on MOEA/D multi-objective optimization was proposed. Taking the human perception error, washout displacement and simulation acceleration error as the optimization objectives, and using the motion space as the restriction condition, the parameters of the washout algorithm were optimized synchronously by adopting the multi-objective optimization algorithm based on decomposition, and the optimal solution was obtained by using the fuzzy membership function. In order to verify the effectiveness of the improved algorithm, a flight simulator motion test platform was established and the washout algorithms with different optimization methods were applied to the platform for comparative analysis. Simulation and experimental results show that the improved algorithm had the shortest return reaction time. Moreover, the phase delay was reduced by 3.5 s, the stability increased by 30%, the sensory peak value was corrected, and the workspace was optimized by 54.6%, so that the simulator has enough movement space and higher dynamic fidelity when simulating extreme motion.