Due to the inaccurate injury assessment model of human body impact, it is hard to reasonably determine the motion speed limit of a collaborative robot in human-robot collaborative operations. In this paper, to achieve a more accurate injury assessment, an improved human-robot impact model is proposed based on equivalent mass-spring-damper model. A damper-spring structure is added between the striker and the object corresponding to ribs with mass, and human heights and weights are introduced to the model to further improve the accuracy and universality. The parameters related to mass were set to be compatible with body heights and weights, and the other parameters were identified through the particle swarm optimization algorithm. The results of the simulation show that the first segment of the improved model response is almost coincident with the test response, and almost the whole interval is improved. This study will benefit the determination of robot motion speed limit and improve the human-robot cooperation efficiency under the premise of safety in the future.