Abstract: On the basis of existing expressways, not only the investment scale is small, but also can meet the growing traffic volume, which is a more reasonable solution to traffic congestion. In this work, the generalized beam lattice method and the space beam lattice method were adopted to verify the accuracy of the calculation method, and the influence of the non-equal space splicing width of main beams on the mechanical performance of splicing width straight beam bridges was also analyzed. The influence of different beam spacing on the transverse distribution of internal forces in straight beam bridges with different width was discussed. The results are as follows. The results of the transverse distribution of internal forces calculated by the generalized beam lattice method are very close to those calculated by the spatial beam lattice method, and the maximum deviation of the influence lines of the transverse distribution of the deflection of each main beam is less than 10%. The non-equispaced width of the main beams will cause the transverse distribution of the internal forces of the main beams of the equispaced straight beam bridge to become uneven. When b_c＜b₀, the difference between the maximum and minimum values of the transverse distribution coefficients of the internal forces of the main beams is 0.533, which is 87.0% larger than the difference between the equispaced width of the main beams. When b_c＞b₀, the difference between the maximum value and the minimum value of the transverse distribution coefficient of the internal forces of the main beams is 0.350, which is 23.2% larger than the difference between the main beams with equal spacing and width. The mechanical performance analysis of the split-width beam of the split-width straight beam bridge shows that: when b_c＜b₀, the bending moment influence line values of the split-width beam are mainly distributed in the negative bending moment region; When b_c=b₀, the bending moment influence line values of the splicing beam are almost evenly distributed in the positive and negative bending moment region; when b_c＞b₀, the bending moment influence line values of the splicing beam are mainly distributed in the positive bending moment region. Therefore, in the design calculation, it is necessary to consider the maximum value of the absolute value of the positive bending moment and the negative bending moment.