Based on the multiple reference frame method and Realizable k-ε model, the whole flow field in a stirred tank with double CBY impellers was numerically simulated using fluent software. The simulation test results were compared with literature. The effects of the blade spacing on the flow field distribution, the lower blade speed and power consumption were examined. The results showed that with the increase of blade spacing, flow pattern from the “connecting flow” into “dispersed flow”, and the test results have good consistency. The influence of blade spacing to the velocity distributions below the upper impellers was relatively large and the influence of blade spacing to the velocity distributions below the lower impellers was little. With the increase of blade spacing, the stirring power increased gradually and the power per unit volumethe decreased.