This article will put much emphasis upon “the Treatise of NirvANa is Unnameable” written by the Venerable Seng Chao. My main goal is to discuss a variety of relevant thoughts and disputes in Buddhism about “the Essential Nature（體性） of NirvANa”. In this article I will also emphasize and explicate the correlation between NirvANa and Buddhist practices and how to confront and understand the crucial philosophical problems arising in the discussion. For the time being, the article has gained the following primary conclusion: Although NirvANa itself cannot be described and narrated by human language, we are still allowed to make use of the conception of the Essence（體） and to express its legitimacy to other relevant thoughts and meaning. To understand the problem of the collation between practices and NirvANa, Venerable Seng Chao considered NirvANa as having not deviated from the practices of Buddhahood, certainly he regarded NirvANa as the way of practice. The position of Venerable Seng Chao supported that after the practice of Buddhahood, every hermit may achieve NirvANa. This is the empirical meaning of the way to NirvANa. But he also supported NirvANa as “letting practice takes its own course,” and “neither something nor nothing”. In this position, he disclosed the transcendent meaning, NirvANa is prior to practice. Some Buddhist scholars considered the Venerable Seng Chao’s concept as so called “gradual enlightenment（漸悟）”. But in this article I refer to the opinion of “dispelling entire accumulated vexation” and then obtaining “instant enlightenment” to achieve the goal of NirvANa. I think of “instant enlightenment” as “complete enlightenment”. The meaning of “enlightenment” is identical to the meaning of “adhigama（證）”. Therefore the opinion of Venerable Seng Chao is one of the perspectives of “instant enlightenment （頓悟）”.