Abstract: The factors influential on nitrate removal in groundwater were studied in laboratory equipment containing unprocessed reed stalks and sand and the rule governing nitrite accumulation was found. The results showed that: ①Negative correlation existed between the TOC and NO-3-N, while negative correlation existed between the NO-3-N and HCO-3. ②Some TOC was demanded if the NO-3-N was to meet the quality standards(20 mg·L-1). ③Nitrite accumulated when the C/N ratios were less than 1.00 and there were some rules between nitrite accumulation and C/N ratios. The optimal C/N ratio was assumed to be 100, at which more removal of NO-3-N is achieved with less excess TOC and NO-2-N in the effluent.