In order to calculate the internal force of prefabricated skew-plate bridge (PSPB), the force state of PSPB with different skew angles is analyzed based on finite element technique. For the side slab, the value of load transverse influence lines of PSPB with different skew angles is obtained, at the same time, the relation between load transverse distribution coefficient and skew angle has been studied. Then a practical formula is derived according to the contrast curve. The comparison diagram of internal force between PSPB and main bridge with the same deck width is established, and a modified formula is deduced. This process provides a new idea on calculation of PSPB, and simplifies the design of PSPB.