The purpose of this paper was the optimization design of heavy strength carriage for 50t heavy-duty truck. Two optimization schemes B and C were provided based on original scheme A, which have different thickness of sole/side plate and main longitudinal girder and different number of strengthening ribs. ANSYS was used to do the finite element analysis of equivalent stress and elastic displacement of truck carriages. The equivalent stress of main longitudinal girder, soleplate and transverse bars of soleplate will increase when the soleplate’s thickness was reduced. The maximum of equivalent stress will increase 13%~15% with 1mm reduction. When the thickness of side plate or the number of side plate’s strengthening ribs was reduced, the elastic displacement of side plate would increase. Scheme C fulfilled the requirement of structure strength, in which the elastic displacement increases in the allowable range and the lightening ratio was 12.6%. Scheme B didn’t fulfill the requirement of structure strength. The numerical results provided theoretical foundations for optimization design of carriage in actual production and the solutions of expansion of carriage.