The Nature of Mind is the core idea of Han Buddhism, especially Chinese Chan (Zen). The founding of Chan began in the early ancestor Bodhidharma and was formed in the Six Ancestors Hui Neng. Traditionally, Mazu Daoyi (709-788) is depicted as a successor in the lineage of Hui Neng, since his teacher Nanyue Huairang is regarded as a student and successor of Hui Neng. Mazu's Chan is easy to educate according to the sentient beings of different roots. While carrying forward the thoughts of the Six Ancestors' Chan, he has also been innovatively developed, thus creating a Hong Zhou school that has far-reaching influence on the later generations of Chan practitioners. This paper intends to discuss the three aspects of Hong Zhou school's concept of the mind-nature : "the truth is in the mind, the truth is in the Buddha" and its corollary "the truth is not in the mind, the truth is not in the Buddha", and finally "the calm mind is the Dao". Mazu Daoyi's Chan thinking faithfully inherits the relevant Chan thought of Hui Neng. Therefore, the Hong Zhou school was an orthodox branch of Chan thinking propagated by Hui Neng and his followers.