Six Sigma DMAIC method was introduced to analyze the engine installation process in order to solve the problem of low first time yield of engine clearance size in aircraft assembly plant C. Multiple regression analysis and other methods were used to determine the key factors affecting the clearance size and their influence degree, and the optimal parameter range was obtained by linear fitting, and a detailed control plan was made. The analysis results of the control chart show that the improved clearance size is in a stable state of the process, and the first time yield of engine installation has increased from 65.2% before the improvement to 95%. Conclusion: Quality control based on Six Sigma DMAIC method has a positive effect on reducing production process variation and improving production efficiency.