Large-scale high-accuracy measurement plays an important role in many applications, such as large-scale equipment manufacturing, space technology and national defense industry. High-accuracy absolute distance measurement by laser is an important research topic in the field of large-scale high-accuracy measurement. And frequency modulated continuous wave (FMCW) laser ranging is a hot point of research nowadays. Because this method is better than pulsed time-of-flight method in measurement resolution, and the problem of ambiguity in measurement, which is the main disadvantage of phase-related method, does not exist. In this paper, the principle of FMCW laser ranging and the main factors reducing the measurement resolution are analyzed. In order to improve the ranging resolution, the method using an auxiliary interferometer to sample the signal in equal intervals of optical frequency is employed. A dual interferometer FMCW laser ranging system is designed and the experiments are carried out. The experimental results show that the measurement resolution is 50 μm at a distance of 10 m.