The observability analysis of the initial alignment problem of the vehicle-based-laser strapdown inertial navigation system (SINS) aided by odometer is carried out. First, the system equation is established by considering the system error items including the odometer scale factor error, inertial measurement unit zero bias, SINS misalignment error angle, etc. Then, starting from system equation, the system observability problem is transformed to the determination of whether there is a unique solution to the state variables of the system. The observability analysis of the system state is conducted by the global observability analysis method, and requirements for maneuvering is given to ensure that the system is observable. Finally, the initial alignment algorithm method and on-track incentive mode are designed according to the results of observable analysis. The simulation of odometer aided laser SINS in-motion initial alignment is conducted by extended Kalman filter, and the simulation results verify the validity of the theoretical analysis.