Xueyu Cave is one of the most famous sightseeing cave in China, what will bring tremendous adverse effect on cave landscape protecting and cave tourism is extremely high P_(CO_2) appearing from April to October. This research used a patented device which could monitor the content of CO_2 in the air and in the underground river at the same time. The process of CO_2's sharp drop in November had been recorded in the continuous monitoring more than two months, and it was found the close correlation between the density of CO_2 in the air of cave and the climate change relevant to temperature and rainfall, while the impact of sightseeing is insignificant, the synchronized change of the degas of underground river and the density of CO_2 in the air totally explicate the dominant effect. The suitable ventilating system and the overall environmental monitoring system were proposed to be established to elevate the feeling of tourists and adapt the sustainability of karst landscape inner cave. Researches of carbon sink in upstream basin of the underground river should be strengthened and an adequate plan to manipulate the carbon input was proposed.