Since 1970s, the normalized difference vegetation index (NDVI) has been widely used in aboveground biomass estimation in natural grasslands. However, there was a saturation phenomenon in NDVI-based estimation model in high-density vegetation biomass, which led to significant uncertainty in grassland biomass estimation. The alpine meadow grassland on the eastern edge of the Qinghai-Tibet Plateau was used to explore the saturation of NDVI based on the ratio vegetation index (RVI), and the impact of NDVI saturation on the spatiotemporal dynamic variation analysis of aboveground biomass was evaluated. The results showed that: 1) Although the accuracy of the aboveground biomass estimation model based on NDVI was higher than that model based on RVI, the sensitivity of the model in high aboveground biomass (biomass greater than 2314.63 kg/hm²) was lower than that model based on RVI. In other words, when the NDVI was greater than 0.73, the estimation model presented a saturation phenomenon (underestimating aboveground biomass); 2) Combined with the RVI, the saturated NDVI was adjusted. Then the optimal biomass remote sensing estimation model was constructed (y=5908.5x-2198.9, R=0.6190, RMSE=902.41 kg/hm²), the RMSE decreased 11.72 kg/hm² than before; 3) From June to early September of the year (161-257 d), the saturation of NDVI-based aboveground biomass estimation model showed extending from southeast to northwest firstly, and then disappeared from northwest to southeast. The average underestimation aboveground biomass ranged from 158.45 kg/hm² to 293.92 kg/hm², and the maximum value occurred in early August (the 225th day of the year), exceeding 600 kg/hm²; 4) In addition, the saturation of NDVI-based model had a significant impact on the analysis of annual dynamic variation in aboveground grassland biomass. After removing the saturation effect, the area where grassland aboveground biomass remained unchanged decrease by 21.44%, while the area with less than -10 kg hm^-2 a^-1 and greater than 30 kg hm^-2a^-1 increased by 8.48% and 16.19%, respectively. This study explored the impact of NDVI saturation on aboveground grassland biomass estimation, provided the theoretical basis for accurate evaluation of alpine grassland biomass and scientific basis for sustainable development of alpine grassland resources.