Under ideal conditions, the LFMCW radar difference frequency signal is a standard sinusoidal signal in the regular region, but a large number of measured signals show that the difference frequency signal contains complex noise signals, which seriously affects the ranging accuracy. The use of analog filters is the most direct way to filter out these noise signals. Aiming at the characteristics of the frequency band of LFMCW radar is similar to the noise band, a simple design method of simulated elliptic filter is introduced. The elliptic function low pass and high pass filter are designed respectively, and then the cascade method is used to form a band pass filter. Experimental results show that the proposed bandpass filter can effectively reduce the noise interference and improve the quality of LFMCW radar frequency difference signal.