Detection optical cable, detection system and detection method for underground detection of oil and gas well

The invention discloses a detection optical cable, a detection system and a detection method for underground detection of an oil and gas well, the detection optical cable comprises a corrosion-resistant stainless steel wire, an aluminum pipe, a cooling pipe and an optical unit, and the cooling pipe is located in the aluminum pipe for introducing a circulating coolant; the plurality of optical units are arranged in the aluminum tube, and each optical unit is provided with a sleeve and a sensing optical fiber arranged in the sleeve. The detection system comprises a detection optical cable, a compressor, a condenser, a connecting block and a one-way valve. The detection method comprises the following steps: when the sensing optical fiber of the detection optical cable does not detect the physical quantity of the oil-gas well, the heat in the detection optical cable is brought out by circulating a coolant; when the sensing optical fiber of the detection optical cable detects the physical quantity under the oil an