The effect of static electric field in smectic layer plane on the helic structure and ferroelectrics of SmC^* liquid crystals is studied by the self-consistent simulation method. The results show that the helic pitch and the average of polarization increase with field strength, the closer to the threshold field, the faster they increase, the tilt angle of director and molecular orientional order parameter increase slowly with field strength and the threshold field decreases with temperature and is related to the helic pitch and polarization without external field.