This paper presents a level measurement system of the frequency modulation continuous wave (FMCW) radar. The procedure is designed by LabVIEW7.0. The system adopts FMCW radar sensor and high-quality data acquisition card. The marine tank level can be measured. For improving the precision of the level measurement, this paper presents an improved algorithm. By using this algorithm, we first adjust the sampling number based on current frequency for meeting the request of the integral period sampling, afterwards, the spectrum is corrected accurately. The experiment is completed by applying the algorithm in LabVIEW. The result shows that the improved algorithm can increase the frequency measure precision for 100 times and more than ordinary algorithms, the measurement error of the level is smaller then 5mm.