The FMCW radar is weatherproof and it can be used in high precision range finder of short distance,especially for the port crane crash preventing system.Based on 8 mm FMCW,the feature of the output signal from the FMCW is analysed.More than that,the details of circuit design for signal processing which is based on DSP is introduced.The circuit can measure precisely,while the signal is filtered,magnified and FFT is analysed.