Abstract: In order to study effect of ambient pressure on the liquid jet of laser-induced bubbles,the collapse time and the water hammer pressure of the liquid jet were obtained after studying the collapse action of the bubbles by means of a fiber-optic diagnostic technique based on probe beam deflection(PBD) in experiments.The data indicate that the collapse time decreases nonlinearly with the ambient pressure increasing,and the water hammer pressure increases nonlinearly with the ambient pressure increasing.At the initial stage of the collapse stage,the acceleration of the bubble wall and the effect of the ambient pressure on the acceleration are very small;at the final stage of the collapse stage,the velocity of the center of the top bubble wall increases very quickly,and the acceleration increases with the ambient pressure increasing at the same stage.It's helpful to underwater laser processing and study about cavitation bubble dynamics.