In the FMCW(frequency modulated continuous wave) liquid level measuring system,the key to measure the distance is to detect the frequency of the sinusoidal echo beat signal.Among the methods to estimating the frequency of the sinusoidal signal,the approaches based on DFT which include the interpolation method with rectangular window and the energy centrobaric correction method are analyzed,and also their advantages and disadvantages.By combining the predominance of the two methods and the analyzing of the influence of the noise on the frequency estimation,a fast frequency estimation algorithm based on FFT is proposed.The experimental results indicate that this approach has the characteristics of high precision,easy implementation and computational efficiency.