Abstract: The paper analyzed and researched power calculation of stator transformer in AC-DC-AC driving system of frequency-conversion speed-regulation of mine hoist, inferred power calculation formulas of hoisting motor and stator transformer in AC-DC-AC driving system, and took two examples to explain power calculating methods of hoisting motor and stator transformer. Finally, it got a conclusion that power selection of transformer in AC-DC-AC driving system has nothing to do with brand and control mode, but has relation to torque of hoist, hoisting speed, factors of motor and converter and efficiency of driving system.