Abstract: Spark discharge is an ignition method for aircraft engines, and studying the energy conversion process of spark discharge in igniters can help improve their performance. In our experiments, a fixed voltage of 4 kV was applied to a spark plug with an electrode gap of 1 mm, and the energy released by the spark plug was changed by adjusting the size of the energy storage capacitor. Moreover, an equivalent discharge circuit model was adopted to calculate spark energy. When the spark energy increased from 0.44 J to 7.87 J, the electrical energy conversion efficiency decreased from 54.99% to 49.23%. Meanwhile, a global model of spark discharge was established, and the electron number density, Electron temperature, and ambient temperature were obtained through simulations. It is found that 40.91%~62.51% of spark energy is converted into the total heat energy of heavy particles, and 0.18%~0.33% of spark energy is converted into the total energy of electrons. By using high-speed Schlieren imaging technology to capture the dynamic process of spark discharge, it is found that the kinetic energy of the airflow is minimal and can be ignored.