The invention provides an alarming method and system and monitoring terminal for an aircraft. According to the alarming method for the aircraft, the outlet temperature of an air conditioner gas compressor, the outlet temperature of an air conditioner assembly and the opening degree of a flow control valve are collected, and when the outlet temperature of the air conditioner gas compressor is higher than the first temperature threshold value, a first alarming message is generated and sent to electronic equipment; when the outlet temperature of the air conditioner assembly is higher than the second temperature threshold value, a second alarming message is generated and sent to electronic equipment; and when the opening degree of the flow control valve is smaller than or equal to the opening degree threshold value, a third alarming message is generated and sent to electronic equipment. The alarming method is used for monitoring the outlet temperature of the air conditioner gas compressor and the air conditioner assembly and the opening degree of the flow control valve, and the alarming massages are sent to the corresponding electronic equipment in a message mode, so that pre-alarm on the outlet temperature of the air conditioner gas compressor and the air conditioner assembly and the opening degree of the flow control valve is achieved, a serviceman is reminded to check and eliminate possible obstacle points in time, and safe operation of the aircraft is ensured.