Objective To investigate the effects of muscles and boundary conditions on head impact response. Methods Three different 3D material point impact models of human head were constructed from the CT scanned images. The first model was the simple head model (SHFr) including skull, membrane and brain, in which the head was free. The second model was the simple head model with muscle (MHFr) including skull, membrane, brain and muscle of the head, in which the head was free. The third model was the MHFr model with shoulder, in which the bottom edge of the shoulder was fixed (MHSFi). The three models were under the impact of a cylindrical lead hammer projected at a speed of 6.4 m/s to simulate the dynamic response of the three models using 3D explicit material point method code. Results The peak values of acceleration of the head centroid for the SHFr, MHFr and MHSFi model were 6.018×103, 4.69×103 and 4.76×103 m/s2, respectively. Conclusions The muscle of the head can disperse distributions of the contact force, enlarge the damage area and relieve the damage of the head. In case of short-time impact, whether the boundary of the head is free or the shoulder is fixed does not affect the dynamic response of the head impact.