This paper presents a method for calculating erodent particle trajectories in slurry flow. It involves computational fluid dynamics (CFD) for calculating fluid phase flow, the discrete phase method (DPM) for capturing the movement of erodent particles, and the volume of fluid method (VOF) for calculating interfaces between fluid phase and gas phase. The method is illustrated by application to a lab slurry jet testing system, which considers free water/air interface tracking, particle size distribution and local particle concentration. The validation of the modeling is done by comparing to a glass bead/water jet testing. Using the proposed method, further parametric studies are performed for calculating actual particle speeds and impingement angles under different operating conditions and physical explanations of the modeling results are provided in the end.