Swamp in the Zoige Plateau which was one of the five main pasture regions in China has been threatened by over-grazing for decades ever since 1960s. In this paper, typical degraded swamp was selected to figure out the main characteristics and critical influence factors under the stress of grazing. On the basis of its water,vegetation and soil information, the degraded swamp was classified into five stages, namely:primary swamp, lightly degradation, moderate degradation, severe degradation and extreme degradation. The degradation characteristics and their influence forces were discussed in this paper. The main characteristics of the degraded swamp water were: (1) TN was higher than normal, (2) TN, NO^-₃, TP, alkaline and the total dissolved solids increased along the degraded gradient,(3)the pH of water is between 8 to 9,(4) HCO^-₃ is the main contributor to the alkaline. The main changes of the degraded swamp vegetation were: (1) an increase of overall species abundance,(2) a decrease in the important values of helophyte, (3) an increase in the important values of mesophyte, (4) Potentilla ansrina replaced Carex muliensis and C. meyeriana as a dominant species in the community. By comparing the similarity between the communities of different degraded swamps,it was found that the rates of vegetation succession decreased along the swamp degraded gradient. The main changes of the degraded swamp soil along the degraded gradient were: (1)a decrease of soil water content, porosity, TN,(2)an increase of bulk density, TP, TK. The vertical changes of different nutrient contents in the soil profile of degraded swamps were complicated. On the whole, the content of TN and TP decreased along the soil depth gradient,and with the increase of depth,the influence of grazing on the content of TP decreased. In order to find out the main influence factors of swamp degradation under grazing, Principle components analysis (PCA) was employed in this paper. Five vegetation variables,eight water variables and six soil variables involved in PCA were simplified into three components which explained 50.77%, 30.50% and 16.72% of the total variables respectively. There was a significant positive relationship between PC1 and Shannon-Weiner index, the importance value of mesophyte as well as the total phosphorus content of soil and a negative relationship between PC1 and importance value of helophyte, Simpons index, water content as well as total nitrogen content of soil. The significant negative relationship between PC2 and pH of water was also observed. Principle components analysis indicated that water physical properties and nutrient of soil were the main driving factors that caused the swamp degradation in the Zoige Plateau. As the nineteen variables changed obviously along the degradation gradient,they were tried to be used to indicate the degree of swamp degradation. According to the three principle components gaining from PCA,a multiple linear regression model was developed based on the three factor scores which could be used to calculate the score of every kind of degraded swamp and it turned out to be useful in degraded swamp classification.