A new method to improve the measuring resolution of a Frequency Modulated Continuous Wave (FMCW) laser ranging system was presented by splicing the sampling signals at an equal frequency interval. The principle of FMCW laser ranging was explored and a fiber FMCW laser ranging system based on dual-interferometric systems was built. In which, the auxiliary interferometric system was used to generate time clock pulses to sample the measured signals at equally spaced optical frequencies and then to splice the sampling signals. By using LabVIEW graphical programming software, a signal processing system was design to detect signal errors, sample and splice signals. The experiments on the ranging system proposed were performed. The results show that the proposed method for sampling and splicing measured signals at equally spaced optical frequencies breaks though the laser scanning limitation and reduces the effect of tuning nonlinearity of the laser source, so it improves the ranging resolution. In the experiments, it offers the range resolution of 70 μm at 8.7 m and the standard deviation of 30 group results is 35 μm.