The invention relates to an 
optical cavity for testing a 
natural gas absorption spectrum. The 
optical cavity is characterized in that the circumference of a gas 
pool is wound with a layer of heat exchange tube; the heat exchange tube is connected with a water tank and an 
alcohol tank, respectively; the exterior of the gas 
pool is sleeved by a heat preservation layer; a base is arranged at the bottom of the 
optical cavity; an air inlet 
pipe, an exhausting 
pipe and a pressure meter are connected to the gas 
pool; an air 
inlet valve is mounted on the air inlet 
pipe; the 
tail end of the exhausting pipe is divided into two paths, a first exhausting valve and a 
vacuum pump are mounted on the first path, and a second exhausting valve is mounted on the second path; a temperature sensor is mounted in the gas pool and is connected with a 
temperature control instrument, and a heater or a refrigerator is connected to the rear part of the 
temperature control instrument. The side surface of the optical cavity is made of 
metal materials, the front and rear surfaces of the optical cavity are made of a 
quartz glass material, the side surface of the gas pool is tightly wound with the cycle of heat exchange tube, the different temperatures of 
natural gas can be regulated by virtue of heat exchange between the 
natural gas in the optical cavity and liquid in a temperature regulation tube, and therefore, the spectral characters of the natural gas at the different temperatures are measured. The optical cavity has the advantages that the measurement is accurate, the structure is simple, the detachment is convenient, materials are easily available, and the like.