The CO2 content and carbon isotopic values are analyzed for natural gas samples from carbonate rocks in Tazhong area. It is indicated that the CO2 gas in some gas samples is organic in origin and the one in other gas samples is inorganic but the hydrocarbon gas is all organic in origin. By comparing with four types of gas samples, it is improved that the CO2 content of natural gas from Tazhong carbonate rocks is generally less than 5, while the CO2 whose content is high is generated by acid fracturing. The CO2 content in the gas samples generated by acid fracturing has a positive correlation to the acid amount and keeps a negative correlation to the production time. According to the analysis data, a correlation chart of maximum CO2 content-acid amount-production time is established. Acid fracturing may bring in increasing the CO2 content in the gas samples but less affects on the N2 and H2S content. The increasing CO2 can affect the parameters related with CO2content but cannot affect those parameters which have no relation to CO2 content. Some suggestions how to use the analysis data of gas samples are finally put forward.