Tracing back to the origin and evolution of public management theory, quantitative research methods based on rational thinking is preferred as important research method of public management. However, due to the ambiguity of discourse system and question about “rational man” assumptions, emphasis on quantitative research methods will lose basis in public management. Moreover, the choice of methods is closely related to disciplinary value orientation. If “efficiency priority”is value orientation of public management, it is not inappropriate to prefer quantitative method research. With the rise of the new public service theory, value orientation changes to “equity priority”, and “democratic equality and citizen participation” is further concerned. Therefore, excessive emphasis on quantitative research methods may deviate from values orientation of public management.