[en] Compared to X-ray radiography, the proton radiography is more suitable for hydro-test experiment because of higher penetration of high-energy proton, and it is easier to gain better result with less uncertainty. The progresses of the proton radiography to form the shadow information inside the object are more complicated. In order to conveniently investigate the proton radiography processes and their characteristics, an empiric formula for high-energy proton radiography is inferred based on the proton's transportation during the radiographic process. The formula contains the terms of elastic scatter and quasi-elastic scatter with multiple scatter process. The validity of the formula is verified by comparing the analytic result from the formula to the result of MC simulation. The results show that the same results are obtained by formula calculation and MC simulation with the Gaussian scatter type approximation, it is about 3%-5% below the more precise result gained by the MC simulation with black-disk model. The research result implies that the formula can take the place of MC simulation to discover the law of the proton radiography and to design the system in some extent. (authors)