To determine the bag filling valve spool box drop height, fluid flow of the filling valve of bag-in-box was analyzed and calculated. The filling valve channel model was pretreated to grid by Gambit pre-processing software. Numerical simulation of the filling valve internal flow field was carried out based on standard turbulent flow model. The influence of descent height of filling valve on pressure cloud of internal speed was calculated by simulation. The influence of descent height on filling speed and sealing effect was analyzed. Fluid analysis was carried out on filling valve using Fluent numerical calculation software. The purpose was to provide theoretical basis for optimal design of filling valve.