The EB reactor (electron beam water treatment reactor) in the form of nozzle jet with relatively large treatment capacity is selected as the research object in this paper. By means of the computational fluid dynamic (CFD) method, both the hydrodynamic behavior and the influence of the EB reactor configuration on the flow velocity uniformity at the reactor outlet are studied, in order to achieve even distribution of flow velocity at the reactor outlet. The results are therefore used to optimize the configuration of the reactor. The study results for the primary EB reactor indicates that there are mainly three key configuration parameters affecting the hydrodynamic behavior of the reactor, including the diameter the reactor inlet, length of the horizontal contraction part and pattern of the bending part. The larger the reactor inlet diameter is and the longer the length of the horizontal contraction part is, the more uniform the velocity distribution of the reactor outlet will be. The optimal reactor configuration parameters are determined as follows: the dimeter of the reactor inlet is 0.2m, the length of the horizontal contraction part is 0.45m, and the configuration of the bending part should fit the flow velocity direction. The numerical simulation results indicate that the hydrodynamic conditions of the optimal reactor are greatly improved, and the flow velocity of the reactor outlet is evenly distributed. Physical model experiment verified the simulation results.