In order to reveal the quantity monotone dependence of the output on the input,a fuzzy monotone dependence algorithm based on decision table is proposed by analyzing the data about the quantity dependence in practice and by applying the fuzzy rough set theory. Then,the concepts such as the fuzzy monotone dependence and the fuzzy monotone increasing dependence membership function are defined by interval mapping,and the parameters and characteristics describing the fuzzy monotone increasing dependence are discussed. Moreover,the correlative proposition is proved. The proposed algorithm is finally applied to the wastewater treatment,with its effectiveness in data mining being verified.