This paper is a further revision and elaboration of one small part of the paper the author presented at the conference on “Inter-sectarian Perspectives of Humanist Buddhism”. While analyzing Master Taixu’s discussion of the principle of religious tolerance, the author proves the possibility and necessity of this principle by examining facts demonstrated in the collected data of Taixu’ 42 successors in Mainland China since 1949. Compared with the religious tolerance and dialogues which have drawn significant attention, this is a new area for further studies. The author argues that the Humanistic Buddhist Spirit shall also guide our understanding of the principle of religious tolerance. To be comprehensive, the principle should encompass four dimensions. Firstly, there need to be better dialogues, communications, and mutual improvement among all Buddhist sects and traditions. It is called concordance in Buddhism, and in practice, it shall be realized in mutual tolerance with diversities of ideas and differences among various sects. Secondly, there should be more tolerance with conversion from one sect to another, or even tolerance with de-robed monastic. Thirdly, there could be more mutual tolerance and support among all Buddhist temples and groups that agree with the ideas of Humanistic Buddhism. Finally, there could be more tolerance and dialogues among all religions.