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It takes a newtype heavyduty truck as study object.Vehicle multi-body model and rigidflexible coupling model with flexible frame were built with FEA method and virtual prototype technology. These models with full loads were simulated in the case of Broad and weighted acceleration mean square root of the driver’s seat floor of cab, suspension dynamic deflection and tire dynamic load were analyzed with different flexible frame, at the same time, these models with full load were simulated in steadystate characteristic test, it was studied that understeer characteristic was influenced by different frame flexibility, and vehicle road tests of ride comfort and steadystate characteristic were implemented. The result showed that simulation results with flexible frame were closer to the experimental results than the ones with rigid frame. With loworder natural vibration frequencies of frame increasing, weighted acceleration mean square root of the driver’s seat floor of cab, suspension dynamic deflection and dynamic tire load became better, that is, vehicle ride comfort was improved. Simultaneously, enhancing stiffness of frame properly could change vehicle understeer characteristic for the better. Consequently, when the frame was designed, enhancing frame stiffness properly or increasing loworder natural vibration frequencies of frame were very helpful to improve ride comfort of heavyduty trucks.