In the drag parachute test， especially during the process of high-speed rocket sled drag parachute test， due to the nonsteady motion of the drag parachute system with a variable acceleration and the influence of wake field in the anterior body， the existing drag parachute test data analysis methods are often difficult to accurately calculate the drag coefficient. In view of the unsteady and wake interference characteristics of the drag parachute test， this paper starts from the dynamic theory of the drag parachute， and theoretically analyzes the additional mass and wake field characteristics of the drag parachute during the unsteady motion. The drag parachute coefficient correction model of the drag parachute system is established by using nonsteady correction and dynamic pressure correction methods. On this basis， the test results of a certain type of cross-shaped single umbrella and cross-shaped double umbrella models are analyzed， the corresponding nonsteady correction coefficients and dynamic pressure correction coefficients are determined， and the cross-shaped single and double umbrella resistance coefficient correction models are established. The results of correction models are compared with wind tunnel tests and traditional calculation methods. The results show that for the single parachute model， the calculation result error can be reduced from the original 27% to less than 9% by the new correction model， and for the double umbrella model， the calculation result error from the original 30% to less than 7%. In this paper， based on the analyses of added mass， the drag coefficient correction method can calculate the drag coefficient of the drag parachute more accurately， so as to provide a more accurate calculation method for the correction of the drag parachute test data.