After presenting an improved theoretical model that describes the dynamic process of optical pulses amplification by the semiconductor light amplifiers (SLAs), both the rising and falling time of amplified picosecond optical pulses by the SLAs have been investigated numerically. The results show that with the increase of the bias current of SLAs, the rising time will decrease and the falling time increase; the input pulse with a large peak power will accelerate the rising time shortening and the falling time lengthening; the gain compression has an obvious influence on the rising and falling time for several picosecond-width input pulses and gives approximately no effect on the input pulses in the tens of picosecond range; the gain asymmetry and shift strongly affect the rising and falling times.