In recent years, dynamic wireless power transfer (DWPT) technology has developed rapidly. Various control methods have been proposed for constant output voltage with the highest possible efficiency in static wireless power transfer (SWPT). For dynamic wireless power transfer system where mutual inductance between the primary and secondary coils changes drastically, output voltage and efficiency depend strongly on the mutual inductance and load condition. In this paper, a novel dynamic mutual inductance estimation method is proposed for DWPT system to realize maximum efficiency while regulating the output voltage. This method is easy to implement because no resonant current or resonant voltage information needs to measure, which is difficult in practical operation. No additional measurement device is required in the system. The simulation results are provided and indicating the effectiveness of the proposed control in a real dynamic wireless power transfer system for EVs.