The zero-stiffness structure has excellent vibration attenuation performance. A new vehicle mounted isolator with negative stiffness spring mechanism (NSSM) and cam-roller spring mechanism (CRSM) is proposed. It has quasi-zero stiffness (QZS) in a small range centered on the initial equilibrium position. Even if the external excitation is strong, this isolator can still maintain stability, and the performance of low dynamic stiffness is not weakened. This characteristic makes the isolator particularly suitable for the vehicle mounted situation. For the harmonic input, the analytical solution of the sprung mass acceleration of the isolator is solved in the time domain. It is concluded that the RMS value and the maximum value of the isolated mass acceleration are proportional to the amplitude of the excitation input. The simulation is carried out and the results show that the theoretical analysis is correct. It also shows that CRMS can effectively suppress the influence of external disturbance without reducing the performance of NSSM, and greatly improve the anti-interference ability of the isolator.