Based on the self-built high-energy ignition device, the engine test was carried out to analyze the cause of unstable combustion of engine during the cold start test and the combustion conditions were studied under different ignition energy. The results show that the stretching length of spark flame arc greatly increases due to the airflow influence and the combustion rate of engine obviously improves with the continuous increase of ignition energy. There is a relatively good correlation between the duration and main combustion period. The number of incomplete combustion cycles and misfire cycles significantly reduces and the cyclic variation reduces from 14.85% to 4.22%. Accordingly, increasing the ignition energy is the effective method to improve the combustion stability and highenergy ignition will be an important research subject for internal combustion engines in the future.