An analytic interfacial stresses solution of hybrid fiber reinforced plastic (HFRP) beam, which is simply supported under uniformly distributed loading, was studied in this article. The analytic solution was obtained with the energy approach, which firstly supposes the trigonometric series of normal stress and shear stress that satisfy the boundary conditions, then ascertains the coefficients of the series by minimum residual energy principle, and finally acquires the analytic solution of interfacial stresses. The presented analytic solution agrees well with the result of mechanics of materials and that of finite element analysis (FEA). Furthermore, based on the analytic solution, four factors affecting the maximal interfacial stresses were discussed, including material and geometry parameters. It is indicated that the primary factors are the ratio of the elastic modulus in the X-direction of the upper-ply to that of the middle part, the ratio of span to height of the middle part, the ratio of height of the upper-ply to that of the middle part; and the secondary one is the ratio of the elastic modulus in the X-direction of the upper-ply to that in the Y-direction.