In order to evaluate the output energy characteristics of the ignition cap， it was proposed to conduct the ignition cap firing test in an open burster container and use a high-speed mid-wave infrared thermal imager to capture the whole process of the ignition cap firing. Since it was difficult to measure the output flame temperature of ignition cap， the drop weight instrument was used to give the corresponding initial firing energy of ignition cap. At the same time， the infrared thermal imager was triggered to collect flame information. The experimental data and infrared images of ignition cap under three test conditions of normal（25 ℃）， heated（50 ℃） and frozen（-49 ℃） temperature were processed. The results show that the output flame maximum temperature can reach up to 1204 ℃， and the flame duration is about 3-4 ms. The whole process of the flame with time can be divided into four stages： firing， diffusion， forming and dissipation， and the temperature in the top and bottom area of flame is much higher than in other areas. Through calculation and software correction， the measurement error of this test is below 6.6%， which can prove the reliability of the method and provide a new way for evaluating the output energy characteristics of ignition cap.