The test data of dynamic load of bridge about impact coefficient nowadays was usually much bigger than the one calculated in the Bridge Specifications, which show that the calculating formulation of impact coefficient in the Bridge Specifications was defective. The working condition, bridge fundamental frequency and excitation frequency of entire truck were taken into consideration, then the correcting calculating formulation of impact coefficient was put forward, which was more accurate and verified by the test data of Dengshidu Bridge. The correcting calculating formulation of impact coefficient is effective for improving the Bridge Specifications in the future.