Since 2015, the inbound visitors of most sources of tourists such as Japan, Russia and Malaysia in China have been on a growing decrease. While the inbound visitors of some sources of tourists such as the United States, Germany and Thailand have only shown some subtle changes. Therefore, China's inbound tourism is facing an increasingly great downward pressure. On the basis of existing researches, this paper screens indicators in light of the economic development of the source of tourists, the appeal of Chinese culture, the economic and trade exchanges with China and transportation costs in China. In consideration of cultural appeal, this paper establishes a new indicator system to evaluate the potential of inbound tourism of major sources of tourists. It finds out the problems in the process of their development and figures out some solutions in order to improve the competitiveness of China's tourism. At the same time, this paper utilizes the principal component analysis to evaluate the potential of inbound tourism for nineteen sources of tourists with the help of cross-section data in 2015. It also ranks in a comprehensive way the major influencing factors of their potential of inbound tourism with direct oblimin. The ranking in order of importance is the rate of outbound tourism, the per capita national income, the proportion of the 25-64 age group, the number of Confucius Institutes, the number of overseas students in China, as well as investment in China. The evaluation result shows that South Korea, the United States and India are the sources of tourists with the highest potential in China. These countries such as Singapore, Germany, Russia, the United Kingdom, Australia, Canada, and France have certain potential to be the sources of tourists. Moreover, Philippines, Indonesia, and Mongolia are at the end of the ranking.