Surface roughness was an important indicator for the formation of surface runoff. This paper takes peat mire of Northeast Jinchuan peat mire as an example, considering impacts of surface slope to measure the roughness index with the chain method in different plant communities. Based on the plant richness, the number of hummock and the coefficient of variation of the hummock forms, we analyzed the mechanism of the changes of surface roughness. The results showed: in three Phragmites australis-Carex schmidtii community, Carex schmidtii community and Betula ovilifolia-Carex schmidtii-Sphagnum palustre community, roughness coefficients changed consistently with changes of species richness and biodiversity of the communities. The changes of the roughness were negatively correlated with number of the hummocks, and positively correlated with coefficient of variation of the hummock forms. It showed that, the smaller the species richness, the larger the ecological dominance;the fewer the dominant plant, the more the number of the hummocks;and the smaller the coefficient of variation of the hummock forms, the more consistence the forming of the micro-geomorphologic relief and the smaller the roughness coefficient. Otherwise, the roughness coefficient became bigger.