Parachute-projectile systems are complex multibody dynamic systems. In order to obtain projectile bodies' state of motion such as displacement and pitch, a parachute-projectile system dynamic model in plane based on projectile body's kinematic equation is developed in Lagrange method. The model is verified through drop tests. Compared the deduced kinematic equation's result and the drop test's result, horizontal displacements and altitudes versus time are approximate, pitch angles versus time are the same in variation trend and approximate in oscillating amplitude and frequency. The result shows the dynamic model can be used to calculate projectile bodies' kinematics in parachute-projectile systems.