The concept of the wave energy converter, developed at Uppsala University is based on a linear generator. Direct pow-er take off mechanism is applied in the system. Optimization of wave energy converter by maximizing its average output power is carried out. In this paper, the passive control by a resistive load is applied in the model. The generator damping force is modelled using the equivalent electrical circuit representation of the generator with the resistive load connected. The resistive load of the outer circuit is the optimized parameter. Matlab function pattern search is used in the optimization algorithm to obtain the optimal for the maximum value of the average output power. The problem is solved for regular plane-parallel waves and the annual average power output is estimated for the wave climate at the Lysekil test site. Cummins equation and State Space Method are utilized to calculate the body motion in time domain.