The wave overtopping forces relate directly to the safety of vertical-wall structure and the decision of the top elevation and funds. Physical models are conducted to research the influential factors for irregular wave overtopping forces. The results show that the key factors are the foundation bed width, the foundation bed height, the height of the parapet to the still water surface, and wave parameters, etc. Based on the least squares method and the multi-varied nonlinear regression model, an empirical equation is fitted about the non-dimensional wave forces and its main influential factors, which may serve as a reference for the engineering design.