acquiring pulse oximetry waveform signals of a patient during CPR process; the pulse oximetry waveform signals are obtained according to light signals penetrated through a finger of the patient; and

determining whether there is ROSC during the CPR process by evaluating characteristics of the pulse oximetry waveform signals; wherein said determining whether there is ROSC during the CPR process by evaluating characteristics of the pulse oximetry waveform signals comprises:

identifying a first spectral peak from the pulse oximetry waveform signals in a frequency domain, the first spectral peak is located at a first frequency corresponding to manual compression during the CPR process;

identifying one or more second spectral peaks from the pulse oximetry waveform signals in the frequency domain, the second spectral peak(s) is/are located at second frequencies different from the first frequency; the second frequencies corresponding to spontaneous circulation; and

determining whether the one or more second spectral peaks are generated by the ROSC of the patient by evaluating time-varying features of the one or more second spectral peaks and/or one or more spectral peak characteristics of the one or more second spectral peaks.