Theoretical analysis of the self-feedback injection locking of the external cavity of the semiconductor laser was carried out. The influence of the self-feedback injection locking of the on-chip microcavity on the output linewidth of the DFB (distributed feedback) laser was studied, and the key parameters determining the locking bandwidth and the linewidth compression factor were analyzed. Based on the back Rayleigh scattering of the on-chip Si3N4 microcavity with a Q value of 2.4×106, the self-feedback injection locking of the DFB laser was realized. The line width is narrowed from 556.71kHz during free-running to 92.28kHz, and the locking bandwidth reaches 425MHz. The research results contribute to the understanding of the self-feedback injection locking mechanism of semiconductor lasers and provide a new solution with simpler structure and higher integration potential for the realization of narrow linewidth lasers.