A plasma processing method is provided. In the plasma processing method, plasma is generated inside a chamber. A DC voltage is applied to an edge ring disposed to surround a substrate while generating the plasma. A first voltage of the edge ring is acquired while applying the DC voltage. Then, the application of the DC voltage is stopped. A second voltage of the edge ring is acquired while stopping the application of the DC voltage. Then, a parameter for controlling the DC voltage is calculated based on the first voltage and the second voltage.