A mathematical model is presented for the performance of an oscillating wave surge converter with a linear electric generator. The model is based on the equivalent electric circuit theory. Equations of pitch motion for the oscillating wave surge converter and a conversion relation between hydrodynamic parameters and their electrical equivalents are employed and a series electric circuit as an adjustable load of the generator is introduced, which give rise to coupled second-order ordinary differential equations governing electric current and voltage drop. The performance of the oscillating wave surge converter is investigated under three load and restriction conditions. The effects of wave frequency on capture width ratio, rotation angle complex amplitude modulus, average absorbed power and electric current phase are examined and the great benefits of a control system are demonstrated. The working process and working principle of the control system and the effect of maximum rotation angle are investigated.