Atom interferometer gravimeter has realized state-of-the-art measurement of ‘g’, thus promising it with broad prospects in frontier scientific research and precision metrology. However, its resolution is limited by different sources of noises, such as Raman phase noise. This paper investigates the Raman phase noise model and its transfer process to the phase of atomic interferometer. We find that signal generator contributes the major part of the Raman phase noise. By calculating the contributions of Raman phase noise to the interferometric phase fluctuation under normal conditions of T & τ, we find that the measurement resolution raises as T increases in the range from 100 ms to 300 ms. For instance, we calculate a contribution of 19.6 mrad/shot to the interferometric phase fluctuation under the condition of T=300 ms & τ=20 μs, corresponding to an influence of 1.35 μGal (1μGal=10-8 m/s2) on the resolution of atomic gravimeter in a single measurement circle.