Combined with trends of strong and moderate reductionism,it can clarify the controversy of reductionism from three different levels:ontology,epistemology,and methodology.The ontology reductionism refers to objects of reality,process and property.The methodology reductionism refers research strategy and method.The epistemology reductionism refers to the reduction of term and theory.Furthermore,the epistemology reductionism is defined by two criterions as the key level.By the criterion of route,the classical reductionism is weakened from constructivetodescriptive,from deductivetointerpretativereductionism.By the criterion of epistemological function,the classical reductionism is weakened from unity of sciencetoreduction for scientific explanation.