Underwater shock can produce very high accelerations, resulting in severe human injuries. In this paper, a shock-structure-human interaction model is proposed to study the biodynamic response of a shipboard sitting subject to ship motion induced by underwater shock (ship shock motion) wherein, the human body is modeled using a lumped parameter system with the parameters obtained from dynamic tensile tests. The results obtained from the human model used in this paper and living human drop test are also compared. Numerical results have revealed the characteristics of human response to ship shock motion. The part in direct contact with the structure (like the pelvis) is much more vulnerable than other parts (like the head). The influences of structural damping and stiffness on the peak loads acting on the human body are investigated. Both damping and stiffness have important influences on the pelvis, but have much less influences on other parts. Injury criteria in the literature are also summarized to facilitate injury assessment.