Chan Master Hwei-si once praised ”saddharma-pundarīka-samādhi” as a unique approach to ”sudden enlightenment in the Mahayana practice”; however, academic studies of this topic rarely discuss it from an empirical perspective based on actual śamatha and vipaśyanā meditation practices. Therefore, this paper shall analyze its distinguishing features so as to explicate the significance of this ”approach to sudden enlightenment in the Mahayana practice” that has been well-acclaimed as supremely mystical and profoundly exalting.This paper analyzes the topic from four perspectives: Hwei-si's personal experiences in meditation practice, scriptural and textual evidences, the requirements to practice Hwei-si's ”saddharma-pundarīka-samādhi,” and a thorough investigation of the concrete achievements attained through the practice, from theories to actual practices.The distinguishing features of Hwei-si's ”saddharma-pundarīkasamādhi” can be concluded with the following five points. First of all, this is a non-sequential approach and practice for highly advanced Mahayana practitioners who are sharp enough and ready for the practice, so it is not for those unequipped bodhisattvas or śrāvaka practitioners (arahats/hearers). Secondly, it is based on ”the attainable practices” of Mahayana approach through faith and vows, which is then furthered as ”un-attainable (formless) practices” and guided by Mahayana wisdom of enlightenment. Hwei-si names it ”the way to bliss in lotus samādhi,” and he further discloses its profound implications in relation to the bodhisattvas' ksānti-pāramitā (forbearance pāramitā). Thirdly, if one can attain extremely profound power of dhyāna samādhi (immensely deep meditative state) so as to enter into ”saddharma-pundarīka-samādhi,” the person can also enter into all other kinds of dhyāna samādhi states attained by the śrāvaka practitioners (arahats). Fourth, with one samādhi attained through ”saddharma-pundarīka-samādhi,” a practitioner can attain infinite samādhi. Fifth, the practice and achievement of ”saddharma-pundarīka-samādhi” can be verified by checking whether the practitioner has attained the state where ”the Six Sense Organs are cleansed and purified” (i.e. purified and freed from any attachment to the vexations generated through the Six Sense Organs).”Saddharma-pundarīka-samādhi” is treated as an ”unbelievable approach to Mahayana sudden enlightenment among all worlds.” With his profound enlightened meditative achievements, Chan Master Hwei-si carefully compared and contrasted the various practice systems and knowledge between the Hinayana and Mahayana traditions, and then turned ”saddharma-pundarīka-samādhi” into a unique approach to attain Mahayana samādhi, an approach which not only contains distinguishing features but also bridges our comprehension and interpretation of the meditative progresses and states between the two traditions. In terms of theoretical discourses and actual practices, he had laid a significant foundation for the future work to construct the Perfect-teachings on śamatha and vipaśyanā meditation practices of Tian-tai School, a task to be completed by Master Zhiyi.