Abstract: Based on multimode rate equations,the relaxation oscillation of vertical-cavity surface-emitting lasers(VCSELs)and edge-emitting lasers(EELs)has been studied through SIMULINK provided by MATLAB.The results show that EELs with multiple longitudinal modes have higher relaxation oscillation frequency and shorter turn-on delay time,which are relatively unchanged for VCSELs case.The simulation results also verify the following conclusions:firstly,VCSELs has the merits of single-mode working and high-speed modulation; secondly,the devices with higher bias current or larger spontaneous emission factor exhibit better temporary characteristics;thirdly,the variation rate of VCSELs'side-mode suppression ratio(SMSR)with bias current is higher than that of EELs.Furthermore,the side-mode intensities augment at the same rate with increasing the spontaneous emission factor,and the main-mode intensity decreases accordingly.Controlling this factor effectively can optimize the single-mode characteristic of VCSELs.