With the development of intelligent cockpit, child occupants will engage in traffic operation in various sitting postures. Therefore, studying the mechanism and risk of whiplash injury of child occupants with different sitting postures has important application value for the research and development of child restraint system. In this study, the 120° and 135° sitting postures of six-year-old child occupant were developed based on the validated 105° sitting posture finite element model with detailed anatomical structure. The whiplash test in Euro NCAP was reconstructed to evaluate the influence of sitting posture angle on the risk of whiplash injury. In the three groups of simulation experiments, the Upper Neck Tension (Fz) was far less than the higher limit of Euro NCAP evaluation although the Fz value increased as the upper torso angle increases. However, the Upper Neck Shear (Fx) and Neck Injury Criterion (NIC) values from the 105° sitting posture exceeded the higher limit of Euro NCAP by 124% and 9%, respectively，increasing the risk of slight neck injury. Neck Protection Criteria (Nkm), NIC, cervical spine stress, and spinal cord stress from 120° sitting posture decreased by 23%, 42%, 56.9%, and 41.1%, respectively, compared with those parameters from the child standard sitting posture (105°). However, the Fx value from 120° sitting posture exceeded the higher limit by 101%; a slight risk of neck injury thus still exists. These assessment parameters from 135° sitting posture decreased by 60%, 50%, 77.6% and 43.6%, respectively, and the parameters were all lower than the higher limit of Euro NCAP. In addition, the maximum von Mises stress was mainly concentrated at the contact position between atlas and axial odontoid (105° and 120° postures) and the posterior arch of atlas with axial odontoid (135° postures). In conclusion, the risk of whiplash injury decreased with the increase of upper torso angle.
