A method and a system for action monitoring of reciprocating sport are provided. The monitoring method is adapted for a monitoring system including a calculation apparatus, at least one gravity sensor and at least one electromyography sensor. The gravity sensor is disposed on at least one motion part of a human body. The electromyography sensor is disposed on at least one muscle part of the human body. The method includes following steps: in a process of a reciprocating sport involving multiple actions acted by a human body, sensing a relative angle of each motion part with respect to a reference of the human body by the gravity sensor and sensing a startup sequence of the at least one muscle part by the electromyography sensor； determining the action acted by the human body according to the relative angle； determining whether a force applied by the human body is correct according to the action and the startup sequence of the at least one muscle part.一種往復式運動的動作監測方法及系統，監測方法適用於包括計算裝置、至少一重力感測器及至少一肌電信號感測器的監測系統，重力感測器置於人體的至少一運動部位，肌電信號感測器置於人體的至少一肌肉部位，所述方法包括下列步驟：在人體進行包括多個動作的往復式運動的過程中，利用重力感測器偵測各運動部位與人體一參考位置的相對角度，並利用肌電信號感測器偵測肌肉部位的啟動順序；依據所偵測的各運動部位的相對角度，判斷人體所進行的動作；藉由動作及肌肉部位的啟動順序判斷人體進行動作的施力是否正確。
