Particles are the primary abrasive media for vibratory finishing, and the contact force embodies the particle action to the finished surface. In this work, the measured and simulated normal forces were compared, the dominant form of particle action on the workpiece's surface was analyzed, and the effect of pipe-cavity's posture on the distribution behavior of the particles-to-wall normal force was investigated. It is found that the measured normal force has the same force characteristic of frequency multiplication as the simulated force, and the simulation results can reflect the finishing pattern. The normal action of particles on the surface, the normal force, can make the cavity surface form a lower surface roughness faster than the tangential action. The posture control can change the distribution behavior of the particles to achieve all-around finishing, and the optimal posture range is >60° in polar and between 60° and 90° in azimuth angle.