In the powered phase, spinning missiles are affected by not only aerodynamic forces and moments, but also variable mass characteristics and jet. In order to investigate the dynamic characteristics of spinning missiles in the powered phase, the jet damping effect was modeled and analyzed. Firstly, spinning missiles were modeled as continuous particle systems. The dynamics equations of spinning missiles considering aerodynamic moments, jet damping effect, and variable mass characteristic were established. Then, the characteristics of the spin speed and coning motion under the jet damping effect and nonlinear variable mass characteristics were theoretically analyzed respectively. Moreover, based on the sufficient and necessary condition for stability of coning motion, the expressions of spin speed, quasi-attack-angle and quasi-sideslip-angle were derived under the combined influence of jet damping effect and aerodynamic moments. Finally, the results of theoretical analysis were verified by numerical simulations. The theoretical analysis and numerical simulation results show that the variable mass characteristics and jet damping effect affect the missile's spin speed and coning motion. To keep spin speed constant, the radius of grain should be slightly smaller than that of the engine nozzle. The jet damping effect increases the damping of coning motion, which is advantageous to coning motion stability. Nonlinear variations of mass characteristics can make cone motions converge faster. The variable mass characteristics and jet damping effect cannot be ignored in design and analysis.