The fundamental principle of cold atom interferometer is analyzed using a novel diagrammatic approach, and the theoretical modeling of space- domain Raman pulses cold atom gyroscope is created. Through the manipulation of approximate mathematical model of the cold atom interferometer, the relationship between the velocity and the transition probability of atom is studied to expound the atom′ s velocity scanning method based on assistant angular velocity sensor. In consideration of precise theoretical modeling, the Raman frequency modulation is used to restrain the Doppler effect and the phase modulation is used to fix the phase relationship in atom′ s velocity scanning method. The numerical simulation calculation results show that the method with compensation and correction can realize rotation measurement with high- precision within the measurement range of the assistant angular velocity sensor.