Based on the schrdinger equation,the interaction between the cold atom and Raman laser pulse is investigated,and the density matrix equation is obtained. The cloud location and velocity of atom under the influence of gravity is calculated by using ABCD propagation matrix for atom beam in space. Using density distribution matrix and propagation matrix of atom beam,the relation between the gravity and the population on the energy level of atom is derived. In the end,the influences of the effective Rabi oscillation frequency of Raman beams on the measurement precision of gravity is discussed in detailed.