Proposed is an optical axis parallelism detection method for pulse laser range finder based on target alignment device. Target reticle center is aligned with the reticle center of visible light optic axis and laser optic axis respectively. Optic axis parallelism deviation is calculated with encoder data. The operation of this method is simple, and it can detect the error of optic axis parallelism in real time quantitatively. The detection accuracy of optical axis parallelism is improved effectively. Thus digital and automative detection is achieved.