In dealing with supernatural facts, the mystics find the experiences that deserve to be described as mystical experience. Mrs. Underhill (1875-1941), the contemporary English mystic scholar, in her extensive research on Christian mysticism, has studied mystical experience. After the great inner transformation, she turned from atheism to deeply religious and mystical beliefs, and by compiling numerous books and articles, was among the most influential scholars of the twentieth century in Christianity. This article tries to explain her perspective about the mystical experience and its realization. It presents a clear picture of its nature by expressing the types, signs and characteristics of the mystical experience. With considering the mystical-psychological doctrines and accepting the role of the subconscious and inner senses, she believes that occurring of the mystical experience through universal and internal journey is possible. In internal journey, the mystic achieves a skill through which he abandons constraints like "for me, from me, me. . . ", and by extending his character, receives an internal revelation. In the course of the external journey, the Salek leads the area of consciousness to the unity through the "discovery of God in creatures". Then he realizes the real presence of unity in the plurality. The main characteristics of the mystical experience are the mystery, inconsistency, the sense of objectivity, the feeling of passivity and irresistibility and awareness of the mechanism of the epistemic layers of the universe. They help to realize the mystical experience.