Abstract: Based on the data from the MOD13Q1 of 7 counties in the Three Rivers’ headwater area of the Northwest of Sichuan from 2001 to 2010,the NDVI cycle of vegetation was analyzed. The results show that the characteristics of NDVI can be well revealed by the wavelet analysis,the significant differences within the study area can be concluded by the t test. In the 7 different counties of the study area,the vegetation was in the slow recovery and the change of vegetation in the same vegetation type was changed by the years,but the vegetation growth cycle and growing period were different under the same type of vegetation and the climate. The vegetation growth cycle fluctuated around 230 days,the difference of vegetation growth cycle in different counties can reach 60 days. The vegetation growing period fluctuated around 110 days,the difference of vegetation growing period in different counties can reach 30 days. The reason was due to differences in temperature in particular months.

Key words: northwest of Sichuan, normalized difference vegetation index（NDVI）, wavelet analysis, t test, the vegetation growth cycle, the vegetation growing period