To study the stress characteristics of wide steel trusses and the stress distribution characteristics of members, taking a wide through steel truss bridge spanning the Xicheng Canal in a national highway as an example, the method of combining the finite element and theoretical analysis is used to discuss the differences between the Code for the Design of Highway Steel Structure Bridges (JTG D64—2015) and the Code for the Design of Steel Structure of Railway Bridges (TB 10091—2017) in the calculation of bearing capacity. And the similarities and differences between the two codes in the verification of bearing capacity and the reasons are further compared and analyzed. The calculation result of the bearing capacity in the highway and railway specifications shows that the results of the strength verification of the upper and lower chords in the highway and railway specifications are basically the same, but there are relatively consistent differences in the verification results of the web members. The difference law in the stability verification is generally consistent with the strength verification. In addition, the railway code formula is relatively simple and easy to use, and it is more economical to design with the railway code.