Diffusers are energy conversion devices in submersible pump structures, and they play a key role in improving the pump performance and operational stability. However, investigations pertaining to the factors influencing the performance of diffusers, in particular the effect of the coupling of factors on the performance of submersible pumps, are still rare. This study focuses on the effect of coupled parameters, such as the inlet angle, inlet width, axial length and number of blades of diffusers, for improving the performance of submersible pumps. First, the orthogonal test method is used to design the diffuser scheme, and sixteen models involving the coupling of different diffuser parameters are established and simulated. Next, the path analysis method is used to extensively understand the effect mode and influence degree of diffuser parameter coupling on the performance of submersible pumps. The results indicate that the mode of action of the diffuser parameters on the performance of the submersible pump can divided into two aspects: the direct action of the parameter itself and the indirect effect of the parameter coupling induced by other parameters. The orders of significance of the parameters affecting the head and efficiency are α 3n > L > b 3 > z and L > α 3n > b 3 > z, respectively. The contribution rates of the inlet angle, inlet width, axial length and number of blades to the pump efficiency are 31.56%, 16.53%, 37.05% and 14.86%, respectively. The numerical results show that the combination of the diffuser parameters-blade inlet angle of 30°, inlet width of 45 mm, axial length of 100 mm and number of blades equal to 8-can help realize the maximum efficiency (83.5%) of a submersible pump with a 18.9 m head. In the production design, the parameters can be quantitatively evaluated in advance by using path analysis. On this basis, the key parameters can be selected according to the order of magnitude of the influence degree. Furthermore, taking into account the production process and manufacturing costs, it is necessary to consider the active role of the non-key parameters in improving the submersible pump performance.