The surface quality of an outer skin part of a vehicle, smooth and with no waviness, is becoming more and more important in today's more and more competitive automotive industry. Strain analysis has been used for formability evaluation and trouble shooting and process optimization has been used for formability improvement in stamping. In this work, diffracto analysis is used to evaluate the surface quality of a stamping part, the strain magnitude and the strain distribution of a part are examined to analyze the root cause of the waviness in the part and process optimization, including optimization of press tonnage, nitrogen pressure and shut height, is used to improve the surface quality of the part. Test results from using different input parameters are compared in this paper. The optimized process parameters have been used in production resulting in more stable and high surface quality and less scrap cost.