In order to get a high dynamic range in pulse signal-to-noise ratio (SNR) measurement and ensure a high measurement accuracy, a research is taken on the calibration of pulse SNR measurement. As we know, a beam will generate multiple reflections with a fixed interval between every two neighboring reflections when it reaches a glass mirror. The light intensity will suffer the degression caused by these reflections. A calibration method for the pulse SNR is provided, and a formula for calculating the multiple reflections from glass mirror is established. Experimental results show that between two neighboring reflections from the back surface, the optical path delays are always close to 24 mm, and the attenuations of relative intensities are always about 10-2. From the analysis on pulse sequence, the dynamic range of the pulse SNR measurement is obtained to be about 2.6×10-8. Furthermore, the effects of material absorption and group velocity dispersion to pulse SNR measurement are also discussed, and it is found that these two factors are neglectable.