Inbound user capacity is an important specification of RDSS system design, which is mainly limited by the inbound signal multiple access interference. To improve the spreading code rate can increase the corresponding inbound capacity. However, the satellite transponder bandwidth limits the maximum spreading code rate, which limits the maximum capacity of inbound signals with a single spread spectrum. As the satellite transponder bandwidth is limited, a spread spectrum separation method was proposed to increase inbound capacity. The situation of separating the spread spectrum into two and three was analyzed respectively. thus obtaining the optimal value of spreading code rate in the both cases. Simulation results show that the existing transponder bandwidth separated into two spreading spectrums can increase inbound capacity 29%, the spectrums which separated in to can increase inbound capacity 37%.