Abstract: To clarify the generation mechanism and influencing laws of self-pulsation in gas-liquid swirl coaxial injectors, this paper captured the self-pulsation phenomenon using atmospheric atomization experiments combined with backlight imaging. Spray images under different operating and structural parameters were obtained. The effects of gas-liquid ratio (GLR), recess length, and gas annulus width on the self-pulsation characteristics were systematically investigated. The results show that the self-pulsation frequency does not change significantly with increasing GLR or recess length, but increases with increasing gas annulus width. The intensity of self-pulsation increases with higher GLR, but decreases with larger recess length and gas annulus width. Injector recess can trigger self-pulsation, and there exists an optimal recess length that maximizes the self-pulsation intensity. Increasing the gas annulus width suppresses self-pulsation, while increasing GLR promotes it. Self-pulsation increases the spray cone angle, and a stronger self-pulsation leads to a more pronounced increase in the spray cone angle.