The concept of valid number of microscopic states is given in this paper, acting as the base on which we discuss the various valid numbers of microscopic states with regard to certain sys-tems under certain circumstances.It is to say that when two systems are different in their independent variables,the valid numbers of their microscopic states are different too. But looking through the ap-pearance to the essence, we can see that these numbers correspond to the number of microscopic stases of the isolated system. We demonstrate that the valid number of microscopic states with regard to sys-tem with specific independent variables plays the role of the characteristic function. Accordingly,through various combinations of various independent variables, we give various valid numbers of mi-croscopic states with respect to various ensembles.