Rice is an important food staple and it is considered a strategic crop after wheat in Iran. Any effort to decrease its loss during harvest time would contribute to self-sufficiency in its production. Grain losses at harvest time and specifically rice crop losses constitute highest level of losses during production process. Combine harvesting losses of rice crop in Iran are 2 to 3 times higher than standard levels elsewhere. Combine platform losses constitute more than 50 percent of total losses, therefore, any reduction in this section of the combine is an important step towards increasing harvest efficiency. In this research, design of a hydraulic system to power platform reel on a rice combine model GUSHENZHIFU was considered in line with efforts to study effect of forward speed and feeding rate on platform grain losses percentage. In the first step current level of reel losses was evaluated working with its current power train system of pulley and belt. Then, a hydraulic system was designed based on power and torque requirement of the reel. The system included an external gear pump, internal gear hydro motor (gyrator), 3-way flow control valve, one-step hand operated pressure control valve, and DC electrical directional spool type valve. System simulation was performed using Automation Studio software and after this stage installed on the platform of the combine. The hydraulic system provided a 10-50 RPM reel speed range with the capability of change in its rotational speed as forward speed changes, an important capability not available not present with mechanical power trains. Power and torque consumption of the reel was measured for various working conditions. At no-load power and torque requirements were 0.072 KW and 15 N.m., respectively. Effects of hydraulic power train, combine forward speed and height of cut on platform losses were determined with a completely randomized design with three replications. A significant difference in platform losses was observed between the hydraulic and mechanical power trains. With hydraulic mechanism lowest rate of losses was obtained at 1.75 Km hr -1 forward speed and 1/4 height level from ground surface. An increase in forward speed from 1.75 km hr -1 to 3.25 Km hr -1 and height of cut from 1/4 to 3/4 crop height resulted in significant increase in platform losses. Rate of feeding crop material which depends on height of cut and combine forward speed was calculated and its relation to platform losses was determined. It was observed that with increase in rate of feeding crop material platform losses increased in both hydraulic driven and mechanical driven power trains. Keyword : Rice combine harvester, Platform, Driven power of hydraulic