The modernized numerical method for the mechanical mixing power calculation is proposed. Proposed calculation method allows to decrease the dependence of a stirred vessel mixing power numerical CFD calculation result on an empirical data by using additional term for considering own inertia of a mechanical mixing device. Proposed method bases on the mixing power consumption calculation technique as the function of a mixing device shaft torque. The verification of proposed method was carried out using the experimental measured and simulated values of the circulation-type reactor pump power. The results of proposed method verification show that non-modernized and modernized methods calculation errors are 3.9 % and 4.8 % respectively. Thus, calculation errors are comparable for modernized and non-modernized methods both. Wherein, modernized method unlike non-modernized does not use error correction coefficient that may be determined experimental only. Thus, proposed modernized method of the mechanical mixing power calculation may be used for engineering design calculations and simulations.