In order to measure the dynamic wavelength of semiconductor lasers under current tuning, an improved method of fiber delay self-heterodyne interferometer was proposed. The measurement principle, as well the beat frequency and dynamic wavelength of recursive relations are theoretically analyzed. The application of the experimental system measured the dynamic wavelength characteristics of distributed feedback semiconductor laser and the static wavelength characteristics measurement by the spectrometer. The comparison between the two values indicates that both dynamic and static wavelength characteristic with the current tuning are the similar non-linear curve. In 20~100 mA current tuning range, the difference of them is less than 0.002 nm. At the same time, according to the absorption lines of CO2 gas, and HITRAN spectrum library, we can identify the dynamic wavelength of the laser. Comparing it with dynamic wavelength calculated by the beat signal, the difference is only 0.001 nm, which verifies the reliability of the experimental system to measure the dynamic wavelength.