Mining dump truck with heavy loads drives on the rough roads, which affects the riding comfort seriously, and the mechanical property of hydro-pneumatic suspension plays an important role in improving the riding comfort. In order to research and optimize suspension mechanical property, the accurate formulas of elastica and damping are established in consideration of the rapid loading, additional and local resistance. Fluent is used to combine volume of fluid model and dynamic grid technique to compare the derived mechanical formulas by simulating the mechanical property. In use of the mechanical formulas, the coupled multi-body dynamics model of this truck, containing flexible frame, is built, and the model is verified by the test data, on account of the maximum error of the seat acceleration up to 8.5%.The suspension parameters are optimized by genetic algorithm, the root mean square of the seat acceleration reduces by 23.58% after optimization, the dump truck’s riding comfort is improved obviously.