Frequency stabilized laser with narrow line width has an extensive application in the industrial production control. However, the Frequency variation of free working semiconductor laser limits the use of laser device. To stabilize the frequency of semiconductor laser, this paper presents a new way which is based on second harmonic absorption characteristics to achieve frequency stabilization of narrow line width diode laser. We have measured the second harmonic signal of water vapor with DFB diode laser of 1.396 μm, and the results show that laser output wavelength drift in 100 hours has been effectively controlled within ±0.16 pm. The absorption peak doesn’t vary with environmental temperature after frequency stabilization. This method is simpler and more reliable and has broad application prospects for frequency stabilization of diode laser.