Hydraulic oil tank liquid level monitoring method and monitoring system and crane

The invention provides a hydraulic oil tank liquid level monitoring method and system and a crane. The method comprises the steps that liquid level information in a hydraulic oil tank and vehicle state information are obtained; according to the vehicle state information, the vehicle working condition state is judged; the liquid level state of the hydraulic oil tank is judged according to the vehicle working condition state and the obtained liquid level information; according to preset alarm conditions, liquid level states are compared, and a decision whether to give an alarm or not is made; and outputting alarm information in response to the alarm decision. The liquid level information of the hydraulic oil tank is associated with the vehicle running state, the operation state and the like, whether the liquid level of the hydraulic oil tank meets the preset alarm condition or not can be judged when the vehicle runs or gets on the vehicle for operation, hydraulic oil leakage can be rapidly recognized, and it is