The classical linear frequency modulation continuous wave(LFMCW) radar ranging method adopts FFT transform to carry out signal processing. Calculation amount increases significantly with the sampling point increasing, which makes the real-time of ranging system not so ideal. To solve this problem, the cross-correlation function ranging method is introduced. Using the characteristics that LFMCW radar signal frequency change is triangular and the echo delay is less than one cycle, the distance can be measured with only one cycle of cross-correlation operation. Combined with the measured value of the cross-correlation function ranging method, FFT transform is used for the partial sampling points of sampling information, and more accurate distance information can be measured quickly and efficiently. The simulation results of MATLAB show that the average ranging measurement error combing with cross-correlation function is reduced by 1.434 m and the average operation time is reduced by 0.5 s, which improves the real-time performance and accuracy of the ranging system.