Abstract: Taking single period injection as an example, the influence of frequency and fluctuation amplitude of the injection field on the dynamics and synchronization of semiconductor lasers are studied numerically. The single period injection is obtained through direct modulation and external modulation, and a modified correlation coefficient called similarity index is used to evaluate the synchronization performance. The results show that injection locking synchronization is realized when injection rate is large enough. In the injection locking regime, similarity index is larger for external modulation than that for direct modulation. If injection rate keeps unchanged, synchronization is little affected by modulation index, but it is affected by modulation frequency. Since outputs of the master l