A nonlinear unrestrained seating human dynamic model is given to simulate seating shipboard personnel.The calculating results of nonlinear model are in good accordance with the human shock experimental results in David Taylor Model Basin(NSRDC).It's shown that the nonlinear model is more advantageous than Payne's linear model.The modified nonlinear seating human model may be used to predict injury probability of seating shipboard personnel to real ship underwater explosion shock.With this model,we can draw up the seating shipboard personnels'tolerance curves to ship shock induced by underwater explosion.