The atomic cooling and trapping process of the cold atom interferometer has high requirements on the linewidth of the laser. In order to obtain a 780 nm laser beam that meets the experimental requirements, the fine spectral lines 5S1/2F = 1 5P3/2F = 3 of the Rb87 ’s D2 line are used as frequency reference, and the modulation transfer frequency stabilization(MTS)method obtains a modulation transfer spectrum without the Doppler background. In the experiment, using this spectral signal as the error signal can stabilize the laser frequency at the rubidium atom reference frequency for up to 20 hours, and the linewidth is enough to meet the requirements of laser cooling atom experiments.