According to the tradition of the Zen Buddhistic school, the sudden method of Hui Neng follows the orthodox teachings of Hung Jen and Tao Hsin, while the gradual method of Shen Hsin is a heresy. The present paper, based on a comparative study of Shen Hsiu’s and Tao Hsin’s way of Zen, shows that the method of “looking at mind, looking at purity” critized by Hui Neng, is espoused not only by Shen Hsiu but also by Tao Hsin. Both Tao Hsin and Shen Hsin adhere to the Zen of the Laṅkāvatāra Sūtra advocated by the earlier Zen masters from Bodhidharma on, but in Hui Neng and the later masters, we find that many ideas derived from the Diamond Sūtra are introduced into the way of Zen. This is the reason why Hui Neng takes exception to Tao Hsin’s and Shen Hsin’s “Lankāvatāra Zen”. Therefore, the distinction between “orthodoxy” and “heresy” in Zen school is not merely a matter of who holds fast to the original teachings of Bodhidharma, there are other factors to be considered.