In order to fabricate the high-power high-bandwidth photodector for radio-over-fiber communication, a optical-to-electrical conversion circuit of cascaded traveling-wave detector arrays for power combining was proposed. Traveling-wave photodiodes were cascaded and connected with inductors based on the structure of traveling-wave detector arrays to obtain high-power high-bandwidth radio frequency signals. The optical-to-electrical conversion circuit was simulated with EDA tools. The simulation results show that the circuit combines the signals of the cascaded photodiodes effectively, which makes the bandwidth increase significantly. The results agree well with the theortetical analysis. In addition, circuits analysis indicates that the frequency bandwidth of the RF signal incereases effectively as the characteristic impendance increases.