Abstract: Using methods of harmonic analysis and partial correlation analysis,based on the SPOT-VEGETATION NDVI of 10 days during the period from 1999 to 2010,we identified the beginning and end time of vegetation growing season for each year in the Three-River source region, and analyzed the temporal and spatial relation between vegetation phenology and cumulative hydrothermal at different times. Results are shown as follows:① The increase of cumulative precipitation and temperature of response time makes start of growing season delayed.② The extremum of partial correlation coefficient between end of growing season and cumulative precipitation and temperature is 0.180 6 and -0.067 8,respectively.It shows that the increase of cumulative precipitation of response time make end of growing season delayed,but end of growing season shift to an earlier date with less impact due to the rise of cumulative temperature.Length of growing season extends and shortens because of the increase of cumulative precipitation and temperature of response time,separately.③ The end of growing season change greatly impacts the annual variation of growing season length. ④ The start of growing season mainly reflect cumulative hydrothermal of the previous year, but the cumulative precipitation of growing season worked powerfully upon the end of growing season.For the growing season length,cumulative temperature before the growing season is the most influential factor.

Key words: vegetation, phenology, hydrothermal condition, growing season, harmonic analysis, fourier interpolation, three-river source region