Based on the concept of local carrier density, intraband carrier dynamic characteristics of quantum well (QW) semiconductor optical amplifiers (SOAs) are theoretically investigated. In our numerical model, electron energy relaxation processes via electron-polar optical phonon interactions are also calculated. It is found that, the electron wave function and the subband energy separation have significant effects on electron energy relaxation rate, especially when the subband energy separation between state |1 〉 and |2 〉 is nearly the same as the longitudinal optical phonon energy, the electron energy relaxation rate in SOAs can be maximized. Finally, for comparison, we analyze the intraband effects in three different SOA samples. The effects of QW designs of SOAs on local carrier density recovery time have been discussed. The recovery time can be reduced to 700 fs from 1.5 ps when the optimized SOA sample is chosen.