System for collecting dissolved gas in geothermal water on site and testing dissolved gas in geothermal water on line and using method

The invention relates to the technical field of dissolved gas extraction of environmental water, in particular to a system for collecting dissolved gas in geothermal water on site and testing the dissolved gas in geothermal water on line and a using method. A system for on-site collection and on-line testing of dissolved gas in geothermal water comprises a water-steam separator suitable for being communicated with a geothermal wellhead; the waterway degassing assembly is connected with a water outlet pipeline of the water-steam separator; the gas path condensation assembly is connected with a gas outlet pipeline of the water-vapor separator; the gas collection assembly comprises a first diaphragm pump, a sampling gas cylinder, a second three-way valve and a detection pipeline, the detection pipeline is communicated with the water path degassing assembly and the gas path condensation assembly, the first diaphragm pump is arranged on the detection pipeline, and the sampling gas cylinder is communicated with the