In order to improve the production process of screw cartridge valve for a hydraulic company, lean improvement was carried out on the production line. Taking the value stream mapping as the main line, the waste in the process was identified and recorded by using Yamazumi chart, and the 5 Whys method was used to analyze the causes of the waste. The ECRS method was used to optimize the production line structure and process to eliminate waste, and the future state map of the value stream was drawn by combining with the standard operation method, and the lean improvement of the production line was achieved. The results show that after improvement, the production cycle is shortened by 34.9%, the work in process inventory days are shortened by 56.8%, the value added ratio is increased by 51.2%, and the production efficiency is significantly improved.