In order to overcome the defect of narrow frequency band and low accuracy exist in the traditional modulation phase shift method, a single mode fiber length measurement technique based on modulation phase shift method was proposed. The single mode fiber length measuring device was designed and developed using the high-speed modulation signal synchronization and high-frequency signal phase difference mearuring technology in the integrated vector network analyzer. An auto-control and data processing software based on VBA plug-in of vector network analyzer was complicated, then an automatic processing method of phase variation was illustrated. Single mode fibers with the length of 2 km, 40 km and 150 km weretested using the developeddevice at different wavelengths, the results show that the standard deviation of 2 km fiber length measuring value is better than 0.2 mm, and the standard deviation of 150 km fiber length measuring value is close to 0.01 m. The fiber distance can be precisionly measured by this device at 1 310 nm, 1 490 nm and 1 550 nm.The proposed device can be expected to provide a new technical approach for precisionly measuring of fiber length.