The pyrotechnic devices are usually used for coercive opening parachutes. Based on the compressible property of flexible parachute textile, a mathematic model is established and the ejection process of parachute bag is simulated in this paper. The calculation results are compared with the results by traditional rigid model and the test results, which shows that the result is consisting well with the test data and the accuracy is improved by the compressible model. The effects of powder parameters, geometry structure of mortar and properties of parachute bag material on the ejection thrust, the parachute bag tension and the tip velocity are investigated. The result shows that the larger original-volume and the less size of piston can decrease the ejecting force, the bag drag is smaller than and lags the tip force for the fabric elastic property, and the higher elasticity and the lower packing density can decrease the tip velocity and the parachute bag tension. The compressible model provides a new designing proposal on pyrotechnic device and parachute bag.