Modulation linearity and modulation range of the tunable laser are the major factors limiting the resolution of FMCW laser ranging. When using a tunable laser with a small modulation range to measure the distance of a single target, the measuring resolution can be improved by fusing signals of multiple measurements sampled with equal optical frequency interval. This method can greatly reduce the FMCW laser range’s demands on modulation range of the tunable laser. This method is easy to achieve and the structural is simple. This system has a wide application in industrial large scale measurement, space technology, and surveying.