This study presents a step toward bridging the gap between numerical simulation and practical applications of parafoil delivery systems. The flexible deformations have an important influence on aerodynamic performance of parafoil. However, the effects of trailing edge deflection deformations under steering operations on aerodynamics and flight performances have rarely been studied. This paper aims to establish a high-fidelity dynamic model for flight simulation of parafoil delivery systems. A fluid–structure interaction method, combining incompressible fluid dynamics solver and structural dynamics solver, was used to estimate the structural deformations and aerodynamic forces. Based on the established model, the flight dynamic responses and aerodynamics of the parafoil system to symmetric control inputs were analyzed. Results show that symmetric deflections can effectively adjust the aerodynamic performance and dynamic behavior. Finally, the airdrop test proved that model predictions are reasonably accurate for use in flight dynamics simulations. This work can be further applied to controller design and parameter adjustment for precision airdrop systems as an alternative to expensive and unrepeatable experiments.