A variety of transition radiators consisting of polypropylene, foam, and sponge materials have been studied for the transition radiation detector in the High Energy cosmic-Radiation Detection (HERD) facility. The test was implemented at the Beijing Test Beam Facility (BTBF) using an electron beam with an energy of 2.5 GeV. It is a simple and effective method that used two identical detectors to study the photon yield efficiency of radiators and it is here denoted as the current ratio method. Based on this method, a parameter χ was defined to evaluate the absolute TR photon yield per electron of the radiator. The polypropylene radiator GXU0.5 300 demonstrated an excellent absolute yield of 4.05 0.97 photons per electron. The experimental results were compared with the corresponding TR generation models in Geant4 and the difference between them in regular radiators was in the range of 1%-7%. The research results of absolute photon yield may provide some reference for future research on radiators.