In order to improve the speed of machine tool spindle and overcome the rapidly wearing off of the conventional electric brush in the rotary ultrasonic machining, research on non-contact power transmission system which based on the principle of electromagnetic induction has been conducted. Through the mutual inductance coupling theory and the simulation on Maxwell electromagnetic simulation software, the non-contact rotary electromagnetic coupling mechanism is established and the influence factor on the transfer efficiency of the rotary mutual inductance, such as rotation speed, inter-stage magnetic gap, matching compensation and the ultrasound frequency has been explored. It demonstrates that transfer efficiency of the energy from the primary to secondary forward load can achieve 80% with proper selection of matching parameter and magnetic gap at a high rotary speed. The electricity intensity in the coil and the magnetic flux shows no significant difference with the acceleration of the rotary speed, while the efficiency decreased with the magnetic gap. Furthermore, it shows that the coupling has an optimal frequency within the input frequency range of the ultrasonic excitation, where the transfer efficiency goes up initially and then turns backward as frequency increased. The research provides a reference for the optimal design of the ultrasonic spindle.