A plasma processing method for performing a plasma process on a substrate in a plasma processing apparatus is provided. The plasma processing method comprises: a sampling-average-value calculating process of sampling voltage detection signals and electric current detection signals and calculating an average value of these signals during a first monitoring time; a moving-average-value calculating process of calculating a moving average value of the voltage detection signals and the electric current detection signals; a load impedance-measurement-value calculating process of calculating a measurement value of a load impedance with respect to a first high frequency power supply; and a reactance control process of controlling a reactance of a variable reactance element such that the measurement value of the load impedance is equal or approximate to a preset matching point corresponding to impedance on the side of the first high frequency power supply.