The aim of the present study was to develop and validate an FE model of neck muscle system according to human anatomy structure in order to analyze the influence of neck muscle activation on head neck dynamic responses and biomechanical responses under rear impact loading condition. A three dimensional neck muscle model was developed on the basis of the MRI data of a 50th percentile male. The model was then combined with a previously developed and well validated head neck FE model in Kriging method. The passive and active behavior of a single neck muscle was defined by coupling Ogden and Hill material models. The neck muscle FE model was validated through volunteer tests of rear impact conducted in Chalmers University of Technology. The result has shown that, compared with non activation muscle behavior, the displacement of head CDG to T1 decreases by 12mm while the angle displacement decreases by 4°, which indicates the significant effect of muscle activation on head kinetic responses. The head neck dynamic responses from the simulations are consistent with the test results. The current neck muscle FE model is of a good biofidelity and can further be used for occupant neck biomechanical research in rear impact loading conditions.