At present， the laser ranging technology is still in the stage that it needs to enter the tracking state to obtain the distance information. Research on the feasibility of the laser ranging technology under the dynamic scanning state is carried out in this paper. By adding a reverse scanning mechanism to the light path and establishing a kinematic model of the light path， the error of the dynamic ranging light path under the scan state is analyzed， and the error index is assigned. The most stringent part in the reverse scanning optical path that needs the strictest control is found. It provides an important technical basis and theoretical support for the development of laser ranging devices in the alert scanning process.