In ultrasmooth surface machining technologies, such as fluid jet polishing (FJP), a better understanding of the material removal mechanism is urgently required for the improvement of surface quality. The shape of the material removal on a polished surface after impact of a liquid jet containing nanoparticles was first measured and then compared with the calculated spatial distribution of the particle-wall collision along the solid surface. The consistency implies that the impact of particles on the workpiece surface is the main reason for material removal in FJP. Thus, to further understand the mechanism of the material removal of FJP, the characteristics of the particle-surface collision of a liquid jet are essential. For this, the effects of jet velocity, particle diameter, and particle density on the particle-surface collisions of a liquid jet were numerically investigated. The results show that the probability of the nanoparticle-surface collision of a liquid jet has a linear relationship with both the jet speed and particle density. Meanwhile, for the particle diameter, the relationship is nonlinear when the particle diameter is <500  nm and has little influence on the collision probability (P_C); whereas, the P_C increases almost cubically when the particle diameter is >500  nm. The present results provide more knowledge about the particle-surface collisions in a liquid jet and may be helpful for further understanding of the material removal mechanism in ultrasmooth surface processing technologies.