蕅益智旭《四書蕅益解》乃疏解儒家《四書》的著作，是智旭為其從學弟子徹因比丘所作，目的在藉由義解《四書》的篇章來彰顯佛教的「第一義諦」。 《中庸直指》為《四書蕅益解》之一，其著作的立意在於顯明佛教的心性之學。從對《中庸直指》的分析可知，智旭主要藉由天台宗的判教與《大乘起信論》「從生滅門返歸真如門」的思想來義解〈中庸〉篇章，並由「開圓解」、「起圓行」、「證圓位」等修學的次第，一方面會通佛教天台與《起信論》，另一方面則會通儒家與佛教義理。本文主要經由對《中庸直指》的探析，討論智旭義解〈中庸〉所使用的方法與特色。

Ou-yi's Explanation of the Four Books (Si Shu Ou Yi Jie) is a work that annotates the Four Books which are canonical books of Confucianism. Master Ou-yi Zhi-xu (1598-1655 A.D.) wrote this book to Bhikkhu Che-yin, one of his students, to highlight the Buddhist Paramārtha-satya (absolute truth) through the explanation of scripts of the Four Books. A Straightforward Explanation of Doctrine of the Mean (Zhong Yong Zhi Zhi) is part of Ou-yi's Explanation of the Four Books, which aims to make known the Buddhist learning of mental nature. Through the analysis of A Straightforward Explanation of Doctrine of the Mean, we learn that Master Zhi-xu explained scripts of the Doctrine of the Mean (Zhong Yong) with the teaching classification of T'ien T'ai Buddhism and the thought of "Return to the Gate of Bhutatathata (True Suchness) via the Gate of Arising and Ceasing" in Mahāyānaśraddhotpāda-śāstra (Awakening of Faith in the Mahāyāna, Da Sheng Qi Xin Lun). Furthermore, this book also realizes the communication between T'ien T'ai Buddhism and Mahāyāna-śraddhotpāda-śāstra as well as the communication between the argumentations of Confucianism and Buddhism through the study order of attaining perfect realization, carrying out perfect practice and achieving perfect status. This essay mainly carries out exploration and analysis on A Straightforward Explanation of Doctrine of the Mean and discusses the approaches that Master Zhi-xu adopted to interpret the Doctrine of the Mean and their characteristics.