Precision measurement using cold atom has surpassed the traditional method, and become an important trend of current quantum precision measurement. Due to gravity, velocity of atoms changes continuously, and therefore, Doppler shift effect should be considered. In this paper, the probability of atom transition and velocity selective effect has been theoretically analyzed and calculated during the Raman pulse duration. Furthermore, the loss of the active atom of π/2-π-π/2 scheme has been estimated, as well as the decay of the fringe contrast caused by atom loss.