The species diversity of plant communities was investigated along the Qinghai-Tibet railway． The results show that the species richness index(S) increased and then remained steady． The Shannon-Wiener index(H)，Pielou (evenness) index(J) were still rising gradually，however the Simpson (dominance) index(D) decreased．The S index value determined to some degree the H index． In the communities with similar S indices，the plant communities with higher J indices were often dominated by the species with higher D index． In the communities experienced secondary recovery on the permanent tundra，the S index，H index，and the J index showed a same tendency:ascending and then descending gradually with increasing distances to the railway． The maximum values of the indices were found at the distance of 75 m from the railroad，and the minimums were found at the distance of 300 m． This indicates that plant communities experienced gentle disturbance showed higher species diversity and become more stable after secondary recovery． The S index changed accordingly with the variations of elevations，as shown by the relationship between the S index and environment factors．