Zen Psychology refers to the psychology of Zen Buddhism as a field of Buddhist psychology. This paper examines the psychology of human beings, focusing on the "Platform Sutra" written by Huineng, the founder of Patriarchal Zen, and the southern Zen school. According to the classification of Buddhist psychology, Zen psychology is divided into theory of Zen mind, theory of Zend mind function, and Zen psychotherapy. In theory of Zen mind, Huineng explains the mind based on self-nature, and explains the theory of dharma, theory of humanity, theory of dependent origination, and worldview though self-nature. Every human mind has its own original character of self-nature. When one's own mind with self-nature is revealed, it is the basic mind. When it is covered, it is the mind of common people. Self-nature is characterized by dharma construction, incompetence, non-naming, cleanliness, equality, and self-Buddhahood. In the theory of dharma, dharma is non-dual and is equal. The theory of humanity is divided into two groups according to the sharpness and dullness or capacity of the human being. From theory of dependent origination, you can see the mobility of cover and revealment, enlightment and delusion, sacred and common. In the worldview, the world and phenomena are the functions of self-nature and one's own mind. The theory of Zen mind function deals with wisdom and defilement of common people. The function of wisdom is to know the whole and one at the same time, and is intangible. Defilement of common people is an inner common people that cover the functions of wisdom. In Zen psychotherapy, in order to eliminate the gap between human and dharma, seeing into self-nature is suggested and the goal. In teleology, the goal is to reveal and see the self-nature covered by defilements. As a methodology from cover to revealment, Huineng interprets the traditional methodology as a new interpretation from the viewpoint of the mind, and presents Sammu as its own methodology. Based on the absence of attachment, Huineng proposed a methodology of No-abiding, No-thought and No-form, to gather mind on reality and treat all things equally. Based on this, Huineng proposed a new methodology for dealing with karma through repentance and vows, and a methodology for edification. In view of the Four Noble Truth, it is the phenomenon that self-nature is covered, the cause of defilement and the mind, the aim of seeing the self-nature which is covered, and the way of revealing the covered self-nature is presented. In this sense, the Zen Psychology of Platform Sutra is psychology of self-nature.