Objective To understand and analyze the relationship between fleas and their indoor small mammal hosts in Yunnan province. Methods During 2009-2013, small mammals were trapped and fleas were collected off the hosts indoor in residential areas in the mountain and dam areas in 43 counties (cities, districts) of 5 different zoogeographical areas of Yunnan province. Levins niche width formula and Shannon-Wiener diversity index formula were used, to analyze the host trophic niche breadth of the fleas and diversity index of fleas and their hosts. Results In total 1925 fleas belonging to 13 species 11 genera 5 families were collected off 1 582 hosts animals belonging to 14 species 10 genera 5 families. Among 13 species of fleas, Paradoxopsyllus custodies, Lentistivalius ferinus, Ctenocephalides felis felis, Monopsyllus anisus and Leptopsylla segnis has higher hosts niche breadth and they were 0.252 5, 0.252 5, 0.252 3, 0.214 5 and 0.202 3. The highest diversity index of parasitic fleas was Rattus nitidus(1.5179), the second Mus musculus(1.3522), and the third R. norvegicus(1.116 6). Conclusion There is no relationship between flea diversity, and diversity and density of host animal as well as richness; to some extent, host niche breadth can reflect the specificity of adult fleas to hosts.