[Objective] The temporal and spatial variation characteristics of vegetation phenology and its response to climate change were analyzed to provide a theoretical basis for regional desertification land control and restoration, and for reconstruction of degraded ecological environment. [Methods] NDVI data for the Mu Us sandy land from 2000 to 2019 were used to determine the temporal and spatial variation characteristics of vegetation phenology and their responses to climate change. The vegetation growth curve was reconstructed using the double logic function method. The vegetation start of season (SOS), end of season (EOS), and growing season length (GSL) were extracted using the dynamic threshold method. Phenology trend was determined by Theil-Sen median and the Mann-Kendall methods. The relationship between phenology and climate was studied by correlation analysis and F test. [Results] ① SOS was advanced by 0.7 day/year; EOS change trend was not obvious; and GSL was extended by 0.75 day/year. ② The multi-year mean value of SOS for vegetation was mainly concentrated at day of year (DOY) 90—140 d, and was gradually delayed from east to west. The multi-year mean value of EOS for vegetation was mainly concentrated at DOY 300—330 d, and was gradually advanced from south to north. The multi-year mean value of GSL for vegetation ranged from 180 to 250 d, and was gradually shortened from east to west. ③ The area of SOS in Mu Us sandy land was negatively correlated with cumulative precipitation in spring (90.81%), precipitation in March (83.85%), and precipitation in April (61.70%), and was negatively correlated with average temperature before the spring season (58.85%), average temperature in March (60.01%), and average temperature in April (51.95%). The area of EOS was positively correlated with accumulated precipitation before the autumn season (54.99%), precipitation in September (63.67%), and precipitation in October (42.34%), and was positively correlated with average temperature before the autumn season (54.95%), average temperature in September (44.70%), and average temperature in October (50.50%). [Conclusion] Over the period during 2000—2019, vegetation SOS was generally advanced, changes to vegetation EOS were not obvious, and vegetation GSL was prolonged. Cumulative precipitation before spring and precipitation in March were the main factors influencing vegetation SOS advance, and precipitation in September was the main factor influencing vegetation EOS advance.