A method for detecting cardiac arrhythmia based on a photoplethysmogram (PPG) signal is provided. The method includes: receiving a PPG signal and a motion signal corresponding to motion of a user； capturing PPG signal segments and motion signal segments corresponding to a time period from the PPG signal and the motion signal, respectively, every time period； filtering out motion artifact noise in the PPG signal segments according to the PPG signal segments and the motion signal segments, and converting the PPG signal segments and the motion signal segments into PPG spectrum diagrams and motion spectrum diagrams, respectively； obtaining an estimated heart rate according to the PPG spectrum diagrams and the motion spectrum diagrams； and determining whether a cardiac arrhythmia exists according to the filtered PPG signal segments and the estimated heart rate本揭露提出一種基於光電容積描記圖(Photoplethysmogram，PPG)訊號檢測心律不整的方法，包括：接收對應一使用者運動的一PPG訊號及一運動訊號；每隔一時間週期分別對上述PPG訊號及上述運動訊號擷取對應一時間週期的PPG訊號分段及運動訊號分段；根據上述PPG訊號分段及上述運動訊號分段過濾掉在上述PPG訊號分段中的運動偽影雜訊，並將上述PPG訊號分段及上述運動訊號分段分別轉換為PPG頻譜圖及運動頻譜圖；根據上述PPG頻譜圖及上述運動頻譜圖取得一估計心率頻譜圖；以及根據上述已過濾PPG訊號分段與上述估計心率判斷是否存在心律不整。
