The deviations of the Priestley–Taylor (PT) coefficient from a fixed value around 1.26 indicate a nonlinear dependence of wet surface evaporation (E) on the equilibrium evaporation (E_rad, which is the radiation term in Penman potential evaporation (E_Pen)). The linear PT equation with a fixed coefficient underestimates E for small E_rad but overestimates E for large E_rad. In this study, the sigmoid generalized complementary (SGC) equation by Han and Tian (2018) was applied to estimate the wet surface evaporation by setting its asymmetric parameter to infinity. The SGC equation with one parameter captures the nonlinear dependence of E on E_rad over the wet surface by including the aerodynamic component of E_Pen and amends the shortage of the linear PT equation. By using datasets over open water surfaces of lakes and ocean, wetlands, and paddy fields, the validation results indicate that the wet surface SGC equation performed better than the linear PT equation on evaporation estimation, especially over open water surfaces, where advections or large-scale synoptic changes are more substantial. The success of the wet surface SGC equation has implications for the extension of the complementary principle to consider above processes.