Abstract: In order to further study the influence of different strut’s structure on fuel/air mixing effect, when it was in the relatively real working condition of scramjet, parts of test system were improved based on the previous work of the research group. Acetone PLIF measurement conditions were carried out in hot test environment, and OH−PLIF measurement conditions were carried out in H₂ combustion environment. The acetone PLIF fluorescence images and the OH−PLIF fluorescence images which were in the multiple cross sections with various working conditions were obtained. The results showed that the acetone PLIF signals of the four kinds of struts in hot test environment were much weaker than cold test results. However, it was still EL1 strut which had best function on fuel/air mixing effect, and that was consistent with cold test results. Under the condition of H₂ ignition combustion, the generated amount and diffusion area of OH reflected that EL1 strut had a better effect on improving the combustion efficiency, and it also reflected from the side that EL1 strut was the best of four kinds of struts.