Wu Zetian (武則天) (625-705), personal name Wu Zhao (武曌), was the only woman in the history of China to be assumed the title of Emperor. In 649, Taizong died, and, as was customary for concubines, Wu Meiniang had to leave the imperial palace and enter a Buddhist nunnery where she had her hair shaved for two years, the Mahāmeghasutra predicted her ascending the throne, and buried with a tombstone without any inscription after her death. All of these were associated with Buddhism. Indeed she was the only woman in the 2100 years of imperial China ever to use the title emperor and to sit on the throne (instead of merely ruling from behind the throne), and this again utterly shocked Confucian elites. Therefore, a great number of scholars have done researches on her from different perspectives. However, there are very few papers explored from the Buddhist perspectives. She was criticized by the people from all the directions, the scholars in particular for ruling a country with Buddhism. Why Wu Zetian, not any other? There should be some special relationship between her and Buddhism. If not, how could she devote all her life to Buddhism? In order to understand the interaction between Wu Zetian and Buddhism, as well as figure out whether Wu Zetian protected Buddhism or damaged Buddhism and vice versa? This paper will collect as many as the facts she had done for Buddhism and the affinities she had created in Buddhism based on the following five chapters-the life of Wu Zetian and her first connection with Buddhism, the relationship between Wu Zetian and Buddha Dharma (apocrapha-the Mahāmeghasutra, Sutra translation and preface composition), the change of the relationship between Wu Zetian and Buddhist Sangha, the interaction between Wu Zetian and Buddhism and Wu Zetian's conversin from Buddhism to Taoism at her old age, and conclusion.