The aim of this work was to provide a basis for security evaluation during transportation process of dangerous substances. The package system (cask body, impact limiter and target) was simplified to a spring-mass model composed of three nonlinear springs and a concentrated mass, then based on the principle of conservation of energy, the transfer course between kinetic energy and strain energy of accident-resistant packaging container was analyzed during impact process, supposing that velocities resulting cask body and impact limiter absorbing the same energy were equivalent, then the equivalent velocity between yielding target and unyielding target during the impact process was studied, and this equivalent relationship was applied in an example. A math method of researching equivalent velocity between yielding target and unyielding target during impact process of accident-resistant packaging container was presented, and then it was validated by an example that when the packaging container collided with unyielding target at a determinate velocity (13.9 m/s) , it was equivalent with a higher velocity (26.8 m/s) colliding with yielding target. This equivalent method introduced in this paper could provide a basis for security evaluation during transportation process of dangerous substances.