The impact of alpine ecosystem degradation to biodiversity and aboveground biomass and the two interaction patterns along with the gradient of elevation are critical for understanding the changes in natural ecosystems that induced by global climate change and human disturbance. This research focused on the degraded meadow and shrub of hillside in the headwaters region of three-river on Tibetan plateau and aimed to investigate their relationship between plant species diversity and above-ground biomass along an elevation gradient. We observed that: (1) the vegetation coverage on the upslope of degraded sloping alpine meadows and alpine shrubs was significantly greater than that on the downslope (P＜0.05). Both degraded slopes of alpine meadows and alpine shrubs exhibited a unimodal pattern of plant species diversity over elevation gradients. Furthermore, the interpretation rate of the quadratic regression equations of the Shannon-wiener index and the Simpson index against elevation gradients on alpine meadow slopes achieved more than 80% and 70%, respectively (P＜0.05). (2) The above-ground biomass of degraded sloping alpine meadows and alpine shrubs was consistent with the altitude gradient, that is, the above-ground biomass of alpine meadows and alpine shrubs increased initially then declined with the increase of altitude. Interpretation rate of the quadratic regression equation indicated that the altitude gradient could accounted for more than 85% of the above-ground biomass in degraded alpine meadows and alpine shrubs (P＜0.05). (3) The association between plant species diversity and above-ground biomass exhibited a similar pattern on both alpine meadows and alpine shrubs slopes, which proved to be a linear increasing trend. The interpretation rate of the regression between plant species diversity and above-ground biomass reached more than 70% on alpine meadow slopes and more than 60% on alpine shrub slopes (P＜0.05). Also, the alpine shrubs on degraded slope land had higher plant community diversity and above-ground biomass than alpine meadow plant communities. The species diversity of plants in degraded alpine, alpine meadows, and alpine shrub slopes, as well as their relation with above-ground biomass, was consistent with the pattern of changes along elevation gradients in degraded alpine mountains. These findings suggest that environmental variations induced by altitude gradients continue to have a stronger influence on plant community species diversity and above-ground biomass. This study has important reference value for understanding the formation ecological mechanism of degraded alpine meadow and shrub of hillside in the headwaters region of three-river on Tibetan plateau and putting forward effective ecological restoration measures.