The effect of gas-liquid momentum flux ratio and recess ratio on the self-pulsation characteristics of gas-liquid swirl coaxial injectors under various backpressure is explored. Atomization experiments were carried out in a backpressure tank by using filtered water and dry air. The spray images for different structures and working condition parameters of the injector were obtained by background light imaging. The dynamic characteristics of the self-pulsation spray and steady spray were compared and analyzed. The results show that when the gas-liquid momentum flux ratio is constant， the spray is more prone to self-pulsation under the ocnditions of low backpressure and small recess ratio. Both recess ratio and backpressure can restrain the occurrence of self-pulsation. Under high backpressure， increasing the recess ratio is beneficial to improving spray stability， but at the same time， the spray cone angle decreases and the spray distribution becomes uneven. When self-pulsation occurs， the spray cone angle increases at first and then decreases with the increase of backpressure， and the spray cone angle is positively correlated with self-pulsation intensity. The spray cone angle is the largest when self-pulsation intensity is the strongest. The steady spray cone angle is less affected by backpressure， but self-pulsation spray is obviously influenced by backpressure. The liquid film first expands with oscillation， then breaks into small droplets and shrinks to the center of injector. The circumferential rotation motion of the self-pulsation process is weak， showing axial oscillation mainly.