This paper starts with study on the transfer characteristics, and the vibration isolation of the cab suspension.The multi-body dynamic model of the vehicle was built in order to analyze the response of the cab suspension. This model includes the cab and its suspension, the power train and its mount, the frame, the suspension, the vehicle-bridge, the steering system and the tires, etc. Design of experiments method was taken to quantitatively analyze the impacts of changing cab suspension parameters.The piecewise function method was used in fitting the characteristic of the air spring. The vibration transmissibility was chosen as optimization objective.The genetic algorithm was used as the optimization method. The analysis results show that there only limited effectiveness on coil spring. So the improvement plans were proposed to replace the coil spring with an air spring and setting transverse damper. According to the plans, the original cab suspension was modified. The piecewise function method was used in fitting the characteristic of the air spring. This method can directly reflect the stiffness characteristic of the air spring within its working area, thus is good for the design and optimization toward different working stage. Meanwhile, the damping characteristic curve of the cab suspension was also designed. Based on the optimization of the modified suspension, there was a great enhancement on the vibration isolation. The lateral and vertical vibration of the seat sliding was decreased a lot. Though the ride comfort analysis, the weighted acceleration RMS value inside the cab was reduced by 29.18%~34.87%. The result shows the optimization and the modification were effective and correct.