The temporal stability of output pulse from the parallel grating pair compressor is discussed under two different conditions. The influence of the beam pointing variance, the retro-mirror misalignment, and the grating pair translational error on the output pulse width from the compressor is quantitatively analyzed by means of numerical calculation. When the grating groove density changes, the sensitivity of the output pulse to these factors is also discussed. Moreover, the allowable tolerance ranges of the aforementioned factors under different conditions are presented.