Taking Xueyu Cave, which is located in Fnengdu county, Chonqing, as an example of the studied subject, the paper monitors subterranean rivers in this region for a long time to collect hydrochemistrical indexes of it. At the same time, parallel study on Shuiming Cave, which also belongs to Xueyu Cave group, is taken. The analysis of hydro-geochemistrical data collected form November 2011 to February 2013 indicates two points: first, subterranean rivers flow through Xueye Cave and Shuiming Cave are the HCO3 -Ca type,a kind of karstic water with low degree of mineralizaiton; Second, hydrochemistri-cal indexes varies with seasons, which is presented as a high PH in dry seasons and a low PH in rainy seasons. To be specific, in rainy seasons, the content of Ca2+, Mg2+ and HCO3 - increase and leads to a good electrical conductivity. In dry seasons, the content of Ca2+, Mg2+, HCO3 - and Ec of Shuiming Cave is higher than that of Xueyu Cave. Therefore, the change envi-ronmental humidity could be estimated according to the variation of [ Mg2+]/[ Ca2+] content, which is affected by the inter-actions between water, soil and rocks during the water movement. Moreover, SIc goes high in dry seansons and keeps low in rainy season . The variation of pCO2 is similar to PH and is opposite to SIc. The SIc is almost above zero around the year, which is beneficial to the carbonate sedimentation. Except the SIc measured in January 2013, it of Shuiming Cave is always higher than that of Xueyu Cave.%以重庆市丰都县雪玉洞为研究对象,对地下河的水化学指标进行长期监测,并选取水鸣洞做平行研究,二者都属于雪玉洞群。通过对2011年11月-2013年2月的水化学结果进行分析得知：雪玉洞地下河的水化学类型为HCO3-Ca型,属于低矿化度岩溶水,水鸣洞水化学类型与雪玉洞相同；其主要水化学指标均表现出明显的季节变化趋势,pH值雨季低,旱季高,与降水变化趋势相反。地下河水 Ca2+、Mg2+、HCO3-浓度和电导率在雨季升高而旱季降低,旱季水鸣洞的HCO3-、Ca2+、Mg2+和Ec值高于雪玉洞；[ Mg2+]/[ Ca2+]表现出旱季较高而雨季较低的季节变化特征,可以反映外界干湿变化,其值受控于洞穴水运移过程中的的水土-水岩作用过程,旱季水鸣洞的值高于雪玉洞；SIc值旱季高雨季低,pCO2的变化趋势与pH相似、和SIc相反,旱季低雨季高,全年的SIc值大部分都在0之上,有利于碳酸盐的沉积,水鸣洞的SIc除2013年1月低于雪玉洞以外,其他月份略高于雪玉洞,相对应的 pCO2低于雪玉洞各监测点。
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