In order to explore the diversity characteristics of bryophytes in the underground forest , we use gradient method to study the diversity of bryophytes in underground forest of Monkeyear Tiankeng, which is about280 meters apart from the earths surface and its diameter is about 300 metres. Research results show that: (1) there are 71 species of bryophytes in underground forest,there are five growth matrices of bryophytes, and the trunk is the most abundant growth matrix of bryophytes (41 species). The number of the other four growth matrix species presents adecreasing trend of forest land >stone surface >carrion> leaf surface. (2) There are 10 species of lifeforms in underground forest, a total of 88% of the lifeform types enjoy the dark and humid environment, while only 12 percent are adapted to the bright and dry environment. (3) Studying on the Margalef of bryophytes, shows that middle (8.461 7)> bottom (7.502 0) > top (6.978 5), and Pielou of bryophytes shows that top (0.945 4) > bottom(0.907 2) >middle (0.844 5). (4) Analysis of the Bata diversity of bryophytes, which shows that the difference of bryophyte community is between (0.75-1.00) in different gradient of underground forest, and the difference between bottom and top is as high as 0.960 8. (5) Analysis shows that the underground forest has high dissimilarity not only in different gradient but also in whole forest, its structure differentiation is obvious and its habitat is complex, all of that is because of its unique topography and hydrothermal conditions. (6) RDA analysis showed that light, humidity and temperature were the main factors influencing the bryophytes species distribution of underground forest of Tiankeng,among which light had the greatest influence. (7) The comparison of species diversity in and out of Tiankeng shows that underground forest of Tiankeng has higher species diversity of bryophytes and it is a natural refuge for the species in karst rocky desertification area.