The invention discloses a method for monitoring a plasma process. The method comprises the steps of placing one substrate into a plasma processing chamber for performing plasma processing, wherein a plasma processing device is connected with an incident light source and a spectrometer; transmitting a background optical signal in a substrate processing process by the plasma, wherein the background optical signal comprises a reference optical signal with a known wavelength; starting the incident light source for transmitting an incident optical signal to the substrate; starting the spectrometer for receiving the reflected incident optical signal reflected by the substrate and the background optical signal, and realizing spectrometer calibration by means of the reference optical signal; calibrating the wavelength of the read incident optical signal by means of the calibrated spectrometer, and obtaining an accurate incident optical signal wavelength; and calculating a substrate processing rate by means of the accurate incident optical signal wavelength, thereby realizing monitoring to the substrate processing process.