Global warming caused by greenhouse gas emissions has had a profound impact on human survival and development. Consequently, this phenomenon has received widespread attention from the international community. Vegetation can absorb greenhouse gases CO₂, and has a huge carbon sink function, so it has an irreplaceable role in slowing global warming. The carbon sink capacity of vegetation has a significant impact on regional and global climate change. Carbon emissions are undoubtedly enormous in the mid and high latitudes of the Northern Hemisphere, so studies on terrestrial ecosystem carbon dynamics and spatial patterns in the arid region of northwest China may provide an accurate assessment how China contributes towards mitigating global climate change and CO₂ emission reduction. The net primary productivity (NPP) and heterotrophic respiration (R_H) in the arid region of northwest China were calculated by using MODIS images, meteorological data, and a vegetation type map, in combination with an improved CASA model and soil microbial respiration model. The NPP and R_H were then used to estimate net ecosystem productivity (NEP) and vegetation carbon sink from 2001 to 2012. Spatial-temporal characteristics and the reasons for NPP and carbon sink variation in the arid region of northwest China were analyzed. The results show that research methods used in this paper were able to quickly extract ecosystem net primary productivity and carbon sink for the northwest arid region. The methods used are efficient, convenient, and practical for large scale carbon balance and carbon cycling studies in this region. Comparison indicated small gaps between simulated and measured site values. The overall difference in the spatial distribution between simulated values and MODIS NPP products is also small, and the volatility of the analog value is less than the value of MODIS NPP products. NPP in the study area showed strong seasonal variation. The maximal NPP value was obtained in July, while the minimum value was obtained in December. In the 12 study years, annual averages of NPP changed minimally. Average carbon sinks showed fluctuating in the 12 years, but increased in general, overall. The carbon sink mean changed from a minimum of 609.04 gC^-1m^-2a^-1 in 2006 to a maximum of 648.02 gC^-1m^-2a^-1 in 2012. The change in mean carbon sink was less than 39 gC^-1m^-2a^-1, with a standard deviation of 11.68. Annual maximum carbon mainly occurred in May, June, and July. Carbon sink fluctuated, but showed an overall upward trend in the northwest arid region between 2001 and 2012. Carbon sink in this region gradually increased from West to East, with Eastern > West > Central. The carbon sink capacity of different natural areas was quite different. The largest carbon sink capacity was recorded in the grassland area of West Liaohe River Basin, while the smallest was recorded in the warm temperate desert region of the Tarim Basin. The annual maximum carbon sink mainly occurred from May to July. Carbon sink was ranked in the order of coniferous forest > farmland > shrubs > broad-leaved forest > grassland > desert steppe.