In CVT, it is essential to optimize Clamping Force in Pulley to improve fuel efficiency. Clamping force in pulley is shaft force to control primary pulley and secondary pulley. It is determined by pulley ratio, input engine torque in CVT and safety factor for protecting belt slip. It is difficult to calculate correct clamping force and detect belt slip. Generally speaking, CVT has a tendency to have excessive Safety factor to prevent belt slip.This excessive safety factor in clamping force leads to lower fuel efficiency. In order to find an optimal clamping force, ‘the minimum clamping force’ which will not induce belt slip should be determined even during decreasing clamping force. Furthermore, clamping force should be maintained near the ‘minimum clamping force’.For this, following logics was developedFirst, the logic to calculate first safety ratio of belt,Second, the logic to detect belt slip state,Third, the logic to calculate the optimal clamping force.This logic was verified and validated on each SILS, HILS and Vehicle. Clamping force control is the backbone in improving Fuel efficiency for CVT. Therefore this study will make a significant contribution to improving fuel efficiency through the ‘optimal clamping force’.