This paper assesses long-term trend of biogenic isoprene emissions in the Three-North Shelter Forest Program, also known as "the Green Great Wall", the largest artificial afforestation in the human history. Results show that the TNRSF has altered the long-term emission trend in north China from a decreasing to an increasing trend from 1982 to 2010. Isoprene emission fluxes have increased in many places of the TNRSF over the last 3 decades due to the growing trees and vegetation coverage.