In order to get radiographic equivalent factor for different materials under different transillumination voltage, the essay used two testing methods of simultaneous transillumination and exposure curve graphic in the environment of 50 kV transillumination voltage,using titanium as standard material. Through the analysis of the steps and problems of simultaneous transillumination method, the essay took in two means of ladder extension and thickness verification as the settlement of the problem. Though the analysis of exposure curve graphic method, the essay affirmed the rules on choosing exposure curve and blackness, explained the relationship between the exposure curve and graphic method. Combined with mathematical tools,the essay obtain the conclusion that the equivalent factor is associated with transillumination voltage, but will not change with the exposure quantity.