The evaluation index system of swamp degradation is an important scientific issue in swamp degradation research. We used Longbao swamp areas to investigate the changes of vegetation during degradation and use principal component analysis method with multiple vegetation indexes to construct the vegetation evaluation index of swamp degradation. The results showed that： (1) the importance value of the helophyte decreased at the degradation process of swamp, but importance values of the hygrophyte and mesophyte had an increase. Carex parva, the dominant plant in the nondegradation and light degradation was succeeded by Kobresia tibetica in the heavy degradation. (2) The diversity index, evenness index and species richness of plant community increased with the degradation of the swamp, and the difference was significant between the nondegradation and heavy degradation (P<0.05). (3) The aboveground biomass decreased significantly with swamp degradation (P<0.05). The belowground biomass in the 0-30 cm soil layer showed a change trend of first increasing and then decreasing with the degradation of the swamp, in which the heavy degradation in 10-20 cm and 20-30 cm soil layers were significantly less than the light degradation (P<0.05). (4) Principal component analysis showed that the nine plant community indices were simplified into the first and second principal components, with the cumulative percentage of variation explained reaching 91.7%. The coverage, aboveground biomass and important values of the helophyte and the mesophyte had a higher load of more than 0.9 in the first principal component, which were well indicators of swamp degradation. (5) The swamp vegetation evaluation indexes (SVEI) are -3.23 ~ -1.98 in the nondegradation, -0.54 ~ 0.51 in the light degradation and 2.15 ~ 3.26 in the heavy degradation, respectively. The present results suggest that the swamp vegetation evaluation index established by using multiple vegetation indexes could well indicate the degradation degree of Longbao swamp. The higher the SVEI value showed the more severe degradation of swamp. SVEI<-1 represented the nondegradation, -1≤SVEI≤1 represented the light degradation, SVEI>1 represented the heavy degradation.