Based on the integral result of the general formula for simple harmonic motion velocity, the timeperiod of the optical beat signal in the half-cyele optical beat counting method is clarified.When analyzing thenumber of optical beats in the initial and final curves of the optical beat signal within a half-eycle, theealculation formulas for the number of light beats in the eurves of maximum value nodes and zero value nodesare corrected using the rotating vector method. Furthermore, based on the relationship between the vibrationvelocity of the moving grating and the period of the oplieal beat signal, a new minimum period method forcalculating weak vibration amplitude is proposed, which expands the approach to calculating weak vibrationamplitude.