In order to meet requirements of transient heat flux measurement and solve the problem that the response time of radiant heat flux meter cannot be accurately measured, we designed a response time measuring device of radiant heat flux meter, which uses the fast response characteristics of high?power laser to form a heat flux step system, uses a high?speed acquisition system to collect the output of the heat flux meter synchronously. The response curve of the heat flux meter is analyzed and calculated to obtain the response time. A variety of response time testing schemes are compared, and the fast response characteristics of the radiation heat flux meter response time measurement device is verified through experiments. The results show that the fastest response time of the device to measure the radiation heat flux meter is 4.4 ms, which can effectively meet the response time test requirements of large?range and fast response radiation heat flux meter, and promote the development of transient radiant heat flux measurement technology in China.