Joint energy dissipation of stepped spillway and flaring gate pier was used in many projects, but the stepped surface damage was recently found in several projects. According to the model test and prototype measurement, the hydraulic parameters such as time average pressure, flow velocity near bottom and aeration concentration possibly affecting the damages of stepped surface under the action of nappe of flaring gate pier were analyzed. In the same time, the method of mechanics of materials was used to conduct force analysis of stepped concrete layers in association with fluctuating pressure and testing data of time average pressure. Results show that, under the conditions of stratifying of roller compacted concrete(RCC) and the damage of surface sealant , fluctuating pressure will act on concrete through surface fissures or interlayer fissures . Thus the maximum tensile stress will possibly occur and when it exceeds tensile strength of concrete, stepped concrete surface is possible to be harmed.