A data processing method includes a period setting step of obtaining a rising period, a stable period, and a falling period with respect to time series data obtained in a substrate processing apparatus, an evaluation value calculation step of obtaining an evaluation value in the rising period, an evaluation value in the stable period, and an evaluation value in the falling period as an evaluation value of the time series data. In the period setting step, a period from when a control signal changes until the time series data falls within a first range including a target level is obtained as the rising period, a period from when the control signal changes until the time series data falls within a second range including an initial level is obtained as the falling period, and a period between the rising period and the falling period is obtained as the stable period.