The finite element method and Smith-Watson-Topper theory are used to improve the rationality of the reliability enhancement test and its results evaluation on proving ground and. The fatigue life of the test car’s front floor is assessed in different velocities, masses and wheelbases by calculating each coefficient of a moderate standard washboard road. Then, the influences of vehicle velocity, mass and wheelbase on the washboard road enhancement coefficient are discussed according to the K-v, K-m and K-L curves. K-v-m and K-v-L surfaces are drawn, and K-v-m and K-v-L regression models are given. The study extends the enhancement coefficient to the enhancement interval, revealing its changing rules with velocity, mass and wheelbase in order to help accurately evaluate the results.