The improvement of the characteristics of grooved-gate MOSFETs compared to the planar devices is attributed to the coer effect of the surface potential along the channel. In this paper we propose an analytical model of the surface potential distribution based on the solution of two-dimensional Poisson equation in cylindrical coordinates utilizing the cylinder approximation and the structure parameters such as the concave coer θ0. The relationship between the minimum surface potential and the structure parameters is theoretically analysed. Results confirm that the bigger the concave coer, the more obvious the coer effect. The coer effect increases the threshold voltage of the grooved-gate MOSFETs, so the better is the short channel effect (SCE) immunity.