Abstract: In order to obtain closed loop control of optical cavity phases in temporal coherent stacking of short pulses, a modified SPGD algorithm with exponential smoothing of disturbance amplitude is applied to control the optical phases of GTI cavity. The influences of the gain coefficient and disturbance amplitude in the algorithm on the coherent pulse stacking are studied. The experimental result shows that the two parameters have similar effects on the pulse stacking. The stacking pulse would trap into local extremum as the two parameters are too low, otherwise, it would oscillate constantly as they are too large. Through optimizing the control parameters, stable coherent stacking is achieved, and the ratio of peak power between main pulse and side lobes is 6.43∶1. The result provides an important reference for the phase control of optical cavity in temporal coherent stacking of short pulses.