The cavitation gain refers to the phenomenon of increasing the number and intensity of cavitation by lowering the threshold of cavitation. Microparticles play a direct and critical role in the cavitation process. Laser cavitation gain based on microparticles has been found. To study the mechanism of cavitation gain, the finite-difference time-domain simulation model is established to analyze the field enhancement effect around the microparticle under laser irradiation. A laser-induced cavitation experiment platform is built, and the pulsation process of cavitation is recorded by a high-speed camera. Combined with FLUENT bubble collapse vector model, the impact of the cavitation water jet on the wall is analyzed. The result shows that microparticles reduce the cavitation threshold of liquid. Owing to the field enhancement effect at the bottom of microparticles, the number of primary cavitation bubbles in the mixed solution is greater than that in distilled water under the same experimental conditions, and the dominant cavitation bubble has a larger radius and a longer pulsation period. The bubble collapse near the wall produces an obvious water jet and wall-leaning effect, and the pressure on the wall in the microparticles mixture is higher than that in distilled water. Cavitation gain of microparticles in the laser-induced cavitation processing is helpful in revealing the mechanism of cavitation erosion and solving the problem of cavitation damage. The behavior of cavitation gain can help us rationally utilize water jet force produced by laser-induced cavitation in microparticle mixtures, which has a profound influence on the innovative development of material surface micromachining.