Two kinds of full-float tractor cab suspension systems based on double crank mechanism and double rocking bar mechanism respectively for a power tractor safety cab was designed. CAD model of the tractor with cab was modeled by using Pro/E. The model was import into ADAMS, and virtual prototype of the tractor with cab suspension system was established. When stiffness and damping of tyres were set fixed, two kinds of suspension system were mounted to the cab. The vibration isolation performance of the two kinds of tractor cab suspension system was studied respectively when stiffness of cab suspension system changed from 20 N/mm to 200N/mm. Both harmonic excitation and a random road roughness excitation were applied vertically to the places where the tyres were mounted. The random road roughness excitation was simulated by using MATLAB/simulink. The simulation results showed that the comfort of the full-float tractor cab with suspension based on double rocking bar mechanism was better than the cab with suspension based on double crank bar mechanism. Therefore, the analysis results provided a basis for designing mechanism of full-float cab suspension system for power tractors.