The stress increment of the in vitro prestressing tendons is of critical importance in the theory of waveform steel web girder bridges. Among the existing stress increment calculation methods, there are relatively few methods suitable for corrugated steel web girder bridges, especially considering the slip effect of prestressed tendons. In order to study the calculation formula for the external prestressed tendon stress increment of composite beams with corrugated steel webs, this paper consider the influence of the slip effect between the external prestressed tendons and the concrete at the steering block. By analyzing the geometric relationship between the deformation of the prestressed tendons and the overall deformation of the structure, the calculation formula of stress increment under symmetrical loads is deduced. Combined with the existing test data, an entity model was established using Ansys, and the nonlinear spring unit Combin39 was used to realize the slip effect of the prestressed tendons; the calculated value obtained was compared with the experimental value and the model value for analysis. The results show that: 1) The calculated value of the deduced stress increment formula is in good agreement with the test value of the corrugated steel web composite beam, which verifies the applicability of this method.2) When considering the influence of the slip effect, the overall deflection and stress increment of the structure increase, and the bearing capacity decreases.