This paper is intended to explore the features of St. Ignatius's mysticism. We begin with the broad and strict definitions of mysticism. Then through the personal experience and special enlightenment described in St. Ignatius's The Autobiography of St. Ignatius Loyola, Spiritual Diary, Select Letters and Spiritual Exercises as well as examples about his experience of spiritual comfort and spiritual pleasure which is gained from his talks and behaviors, we show not only St. Ignatius's passion and enthusiasm about God but also the fact that he was indeed a mystic with mystic experience in both the broad and strict sense. Then, we further explore the important features of St. Ignatius's mysticism through discussion about his mysticism of holy trinity, the mysticism with Jesus as the center, the mysticism of service, and the mysticism of churches. By investigating the context of his mysticism, we bring out the contemporary meanings of his behaviors and thoughts, which profoundly enlighten Christians' mystic spiritual formation.