The globally averaged combined land and ocean surface temperature show a warming of 0.85℃ over the period 1880 to 2012. This phenomenon is mainly due to the burning of oil, gas, coal and wood for energy since the industrial age. Climate change has already affected the carbon cycle of terrestrial ecosystems. An obviously observable effect of such ongoing changes is the timing of phenology events, such as bud-burst, flowering, leaf unfolding, and leaf coloration. Phenology studies based on ground and remote sensing observation indicate that the length of vegetation growing season has significantly increased over the past decades, principally through an earlier beginning and a later termination. So it is necessary to study the effects of changes in growing season length on gross primary productivity (GPP) of terrestrial ecosystem under the global warming in the middle and high latitude. Northeast China is located at middle latitudes in the northern Hemisphere and is an area that exhibits prominent climate changes. Boreal Ecosystem Productivity Simulator (BEPS) is an ecological process based model, which originally stemmed from the FOREST Bio-Geochemical Cycles (FOREST- BGC) model. This model includes photosynthesis, energy balance, hydrological, and soil biogeochemical modules. Stratifying canopies into sunlit and shaded leaves, it incorporates a new temporal and spatial scaling scheme into Farquhar's instantaneous leaf biochemical model to calculate daily carbon fixation. In this article, firstly, we run BEPS model, combined with meteorological data (including maximum and minimum air temperatures, precipitation, relative humidity and solar radiation), remote sensing data and soil data to simulate the spatial and temporal distribution of GPP in Northeast China during 2001-2010. Then, we analyzed the change of growing season length and its effect on GPP in Northeast China from 2001 to 2010. The results show that: ① There are no significant trends in the start, end and length of growing season in 2001-2010 (R~2≤0.22,P≥ 0.17) in Northeast China. The length of growing season is more affected by the start of growing season, and the start of growing season have a significant correlation with spring temperature (R2=0.74,P=0.001), so we can conclude that the length of growing season is mainly affected by spring temperature. ② The terrestrial ecosystem's annual mean GPP is about 1 057.844.6 TgC in Northeast China. There is about 1 032.245.8 TgC GPP in growing season, accounting for 97.5% in total. It means that Northeast China's GPP is mainly sequestered in growing season. ③ The interannual variation of GPP is not significantly affected by the change of growing season length, it is mainly regulated by precipitation in Northeast China. And the response of the main vegetation type to phenology is consistent with that of the whole Northeast China. However, there are also some uncertainties in GPP simulation and in growing season length definition, so we should take more models to simulate GPP and use more methods to define the length of growing season in the future research.