In order to explore the factors influencing the hydrodynamic performance of an H-type straight-blade tidal turbine, based on theoretical analysis, a three-dimensional model of an H-type straight-blade tidal turbine was established using large-scale modeling software UG, and three-dimensional numerical simulations were carried out using the Fluent software and the sliding mesh method. Under the conditions with the same airfoil type of H-type turbine blade and the same turbine solidity, the hydrodynamic performance of the tidal turbine was analyzed by changing the number of runner blades and inflow velocity. The results show that the number of blades has a significant effect on the hydrodynamic performance of the H-type straight-blade tidal turbine. The greater the number of blades, the smaller the output torque is. When the number of blades is three and the tip speed ratio is 1.63, the highest turbine power coefficient is 31.21%.