Abstract: Based on the basic principle of sliding grid method, a new concept of sliding period was proposed and used to simulate the flow fields in stirred vessels with novel combined inner and outer agitators which are rotating in opposite directions.This work was compared with dual pitched paddles and anchor agitator.The velocity fields, mean velocity components, rates of velocity change, shear rates and axial circulation capability were analyzed.The results showed that the use of the concept of sliding period could reduce the CPU time to a certain degree. By using the novel combined inner and outer agitators, the radial and axial flows were strengthened. The combined inner and outer agitators could improve the flow fields near the vessel wall, and work better for pseudo-plastic fluid than Newtonian fluid. In addition, the shear strength and axial circulation capability of combined inner and outer agitators were higher than dual pitched paddles.