Digital down conversion for wideband signal is introduced based on polyphase filtering,optimizing the existing implementation scheme. Wideband signal is sampled by the ADC12D1800 and the output signal is divided into several groups,which can achieve achieves digital down conversion and decimation combined with polyphase filtering. This method can effectively reduce the data rate and the data processing speed,solving the problem of the mismatch between the high sampling rate and low processing speed. This design is simulated in Altera Stratix IV FPGA,and compared with the traditional DDC. The result shows that the benefits of the optimization for architecture of DDC includes lower operations amount,less consumption of FPGA resource. The new scheme is feasible and practical.