The qualitative researchers adopt various paradigms (named positive, constructive, and critical) to do their researches. Besides stating their own methodology and employing the criteria of qualitative researches, they should follow the criteria belong to its own paradigm as well. In this paper, we investigate the criteria of qualitative research firstly. Then we discuss how each paradigm deal with the validity of qualitative research. Finally, we state the evolution of validity under these three various paradigms/perspectives of social science.