The equivalent Markov motion model (EMMM) is used to improve the probability model for solid particle erosion and droplet deposition. When calculating the solid particle erosion, the probability density distribution of particle velocity developed by EMMM is used to improve the solution of the impact parameters of solid particles. When calculating the droplet deposition rate of annular flow, the conversion coefficient proposed by EMMM is used to correct the variance of the particle displacement. The proportion of the particles deposited is calculated by solving the probability of a single particle reaching the pipe wall or liquid film. The improved model involving the EMMM is well verified by comparison with experimental data. Compared with the previous probability model, the present model can provide more accurate predictions. In addition, the self-compatibility of the EMMM is discussed in detail.