The objective of the present disclosure is to provide a method of expanding the sheath and bulk of plasma using dual high frequencies, in which the sheath and bulk of microwave-generated plasma are expanded. The method of expanding the sheath and bulk of plasma using dual high frequencies according to one embodiment of the present disclosure includes: a generation step of generating plasma by a microwave plasma generator; and an expansion step of expanding the sheath and bulk of the plasma by applying a radio-frequency (RF) bias to a radio-frequency electrode disposed at a predetermined distance from the microwave plasma generator.