A novel six-blade grid disc impeller (RT-G) was designed and the single-phase turbulent flow and mixing in a baffled stirred tank agitated by this impeller were numerically studied by detached eddy simulation (DES) model. For comparison, a standard Rushton impeller (RT) with the same dimension was also investigated. The numerical results were compared with the reported experimental data and good agreements were obtained. Comparisons of the mean velocity, turbulent kinetic energy, power consumption and mixing time of RT and RT-G were performed. Results show that, for the tank stirred with RT-G, the velocity components can be increased in comparison with RT when the same power is consumed. The increase of the turbulent kinetic energy is about 20-30%. Besides, the mixing time for the tank stirred with RT-G is about 11% shorter than that of RT stirred tank operated at the same condition.