Abstract: Planar laser-induced fluorescence (PLIF) technique is utilized to measure the images of hydroxyl radicals (OH) fluorescence and spontaneous emission in hydrogen/air and kerosene/air supersonic combustion. The results show that PLIF has been an efficient approach for identification of fuel/air mixing and combustion process. It is found that large number of OH radical is concentrated in the cavity range of the combustor, it is helpful to understand the mechanism of the cavity as the flame-holder in supersonic combustor.