In order to achieve accurate measurement of close range targets and make full use of the excellent characteristics of Linear Frequency Modulated Continuous Wave (LFMCW),a millimeter wave LFMCW radar ranging system is designed based on ARM single chip.The system adopts the structure of “ARM+Phase-Locked Loop (PLL)+RF transceiver”,uses STM32F3 series ARM MCU as the main control chip for controlling the PLL and 77 GHz RF transceiver chip to complete the transmission and reception of the LFMCW signal,and uses the ARM internal ADC to perform IQ dual differential sampling on the intermediate frequency echo.The Fast Fourier Transform (FFT) is implemented inside the ARM to extract the target distance information.When the bandwidth of the modulated signal is 3.2 GHz and the period is 2 ms,the radar system can implement high-precision ranging to the targets within 2 m with an error less than 0.03 m.The experimental results show that the system can effectively detect short-range targets by transmitting broadband LFMCW signals,and has the advantages of high detection accuracy,strong versatility,good reliability and small volume.