Abstract: To make the design weight of the carriage of heavy-duty truck lighter, the FEA software ANSYS was applied to the numerical simulation of the changes in structural strength and rigidity after using the 600MPa high-strength platform floor plate instead of the Q345B plate. The results showed that making the high-strength plate in different use under the action of 50t static load, the equivalent stress in the main longitudinal bearer is maximum, while that in the outer stringer and floor's cross reinforcements is less, with the minimum at the bottom/side/front/back plate. The 600MPa floor plate can meet the requirement for structural strength of which the margin is around 130MPa, and no margin can be found for Q345B plate. The maximum and minimum of total elastic displacement are found at the middle/upper part of side plate and the middle part of bottom plate, respectively, and, as a whole, the total elastic deformation of the carriage made from the 600MPa plate is greater than that made from Q345B because of the reduced structural rigidity due to decreased plate thickness. The simulation results have been applied in actual production, and the weight of truck's carriage is therefore reduced by about 21% with tonnage capability improved somewhat. A theoretical foundation is thus laid down for further investigation and practical production.