The power consumption of a coaxial mixer consisting of an outer anchor and different inner impellers was experimentally characterized in an agitating vessel full of Newtonian fluids (highly viscous malt syrup). Meanwhile, taking the rotation mode, speed ratio, and diameter ratio between the inner and outer impellers into consideration, a novel correlation for the calculation of the total power consumption of the coaxial mixer was introduced by defining a new characteristic diameter and a new characteristic speed. The results show that the inner impeller has an obvious effect on the power consumption of the outer impeller: the power consumption of the outer impeller will decrease under co-rotation mode and increase under counter-rotation mode. The power consumption of the high-speed inner impeller accounts for a large percentage of the total power consumption and the outer impeller has little effect on it. Compared with other existing correlations, the Reynolds number calculated from the novel correlation is greater and the power number is smaller, which can better reflect the high efficiency and low power consumption of the coaxial mixer.