Carbon dioxide flooding well three-in-one intelligent monitoring system and monitoring method

The invention discloses a three-in-one intelligent monitoring system and method for a carbon dioxide flooding well, and the system comprises a wellhead connector which is fixed at a wellhead casing gas sampling port, carries out the sampling of casing gas, measures the pressure value of the casing gas, and receives a liquid level reflection wave signal; the automatic liquid level tester is used for manufacturing compressed air as an external pressure type sound production energy source and measuring the depth of the liquid level; and the gas on-line monitor is used for detecting the casing gas collected by the wellhead connector and measuring the carbon dioxide concentration value of the casing gas. The wellhead connector is connected with a casing sample gas joint, a casing gas electromagnetic valve for producing sound under internal pressure, a compressed air electromagnetic valve for producing sound under external pressure and a microphone for receiving echoes are mounted in the inner cavity, and internal