Abstract: Chemical and microbiological indicators were used to explore the conduits of underground water medium and the recharge of underground water in a typical karst valley in Chongqing,China.High resolution tracer tests of two times with uranine have been conducted to find out the conduits of underground water medium and its recharge.Classification with Cl-concentration and discharge of the water in different sampling sites were used to divide the rainy reason and dry season specifically.With the results of classification,the correlation coefficient of nitrobacteria,denitrifyimg bacteria,which were the microbe indicator and NO-2,NO-3 in different season,were analyzed.Using the chemical indicator tracking curves,which had only one peak without any tale,the recycle ration of uranine was calculated to be 93.94% and 27%,and the ration between the maximum apparent velocity and the average apparent velocity was 1.26 and 1.12.Therefore,chemical tracking implied that there was a big conduit underground river without big ribbon or byroad.Classification showed a rainy season lasting from May to September,the rest of the year was a dry season.In the dry season,at the output（site S2） of the underground river,the correlative coefficient of nitrobacteria and NO-3 was 0.929.The correlative coefficient of denitrifyimg bacteria and NO-2 was 0.811,but such relation has not been found in the rainy season when the correlative coefficients were 0.153 and-0.311.On the other hand,at the income（D1） of underground rivers, the relation of microbe and NO-2,NO-3 has been found neither in the dry season nor in the rainy season.In a word,microbiological tracking implied the main recharge of the underground river in a dry season was the soil penetrative water through the fissures in karst,but in a rain season,the main recharge was surface water flow through swallow holes.