In order to reduce the frequency noise of Raman laser, a phase-frequency double-modulation frequency stabilization technique is proposed. The laser is modulated by a fiber electro-optical phase modulator (F-EOM) and large-detuned sidebands are produced. Radio-frequency(RF) signal is used for frequency modulation of the microwave driving signal of F-EOM, and one of the large-detuned sidebands is locked to a saturation absorption spectral line of rubidium atoms by lock-in amplification. The frequency stabilization and 2 GHz frequency shift of Raman seed laser are realized by using this technique, and the linewidth of Raman laser is narrowed down to 56 kHz. The single measurement noise of atom gravity interferometer induced by Raman laser frequency noise is expected to be reduced to 7×10-9 s-2.