Abstract: In order to improve the hydraulic performance of large-scale low-lift bidirectional flow channel pumps, based on the elliptical profile design of the outlet diffusion section of the flow channel, combined with the SST k-ω turbulence model, the influence of the diameter parameters of the outlet diffusion section on the hydraulic performance of a bidirectional flow channel pump was discussed. By adjusting the maximum diameter D₁ of the horn tube of the outlet conduit, the maximum diameter D₂ of the water guide cone respectively, and adjusting both at the same time, the distribution rules of the flow velocity uniformity, hydraulic loss and kinetic energy recovery rate of the outlet conduit under different diameter schemes were compared. Combined with the entropy generation theory, the influence of outlet diffusion section diameter on the hydraulic performance of the bidirectional flow channel pump was revealed. The results showed that when only the maximum diameter of the horn tube D₁ increased, the maximum efficiency of the pump device increased first and then decreased. When D₁ = 2.09D₀ (impeller diameter of the pump device), the efficiency of the pump device was the highest, and the hydraulic loss of the outlet channel was reduced by 1cm compared with the initial scheme. When only the maximum diameter of the water guide cone D₂ increased, the hydraulic loss of the outlet passage decreased first and then increased. When D₂ = 2.09D₀, the hydraulic loss of the outlet passage was the smallest. When D₁ and D₂ increased at the same time, the maximum efficiency of the pump device gradually increased, and the maximum efficiency of the pump device gradually increased at D₁ = D₂ = 2.2D₀, and the hydraulic loss of the outlet channel was reduced by 1.8cm compared with the initial scheme. The research results can provide reference for the optimal design of the bidirectional flow channel pump device.