To reduce the ejection load and improve the launch accuracy of rockets， a telescopic canister gas ejection system was proposed. The dynamic characteristics of this ejection system were studied based on theoretical analysis and numerical calculation. The maximum relative error between the simulated and theoretical velocities of the rocket exiting the canister was -0.98%， and the accuracy of the finite element model of the ejection system was verified. Based on the finite element model， the depressurization effects of the ejection system and the effects of launch angle， thrust misalignment， and wind load on the rocket’s motion attitude and the inner canister’s vibrational response were investigated. The results show that compared to the single canister ejection system， the average and maximum depressurization effects of the ejection system are about 30.3% and 35.1%， respectively. Larger launch angle， thrust misalignment， and wind load indicate worse motion attitude of the rocket and vibrational response of the inner canister. The launch angle is the main factor affecting the launch accuracy of the rocket， and the maximum effect of the launch angle on the launch accuracy is 2.3 to 4.4 times that of the other two factors. The research can provide references for the design and optimization of telescopic canister gas ejection systems.