Abstract: 【Objective】The Loess plateau is in the transitional region from wetness to dryness, from forest to grassland, from farming to animal husbandry, being the sensitive zone in climate change and agricultural development in China, the research on phenological feature of surface vegetation coverage in the region is of directive significance to agricultural production, environmental protection and ecological construction. Analysis of difference in phenological trends of vegetation in different time series and altitudes and hydrothermal conditions shall offer theoretical support and decision basis for current agricultural ecological environment improvement and sustainable development on loess plateau.【Method】Phenological feature values of vegetation on Loess Plateau every year were determined and phenological change trend was analyzed based on NDVI of ten-day values of SPOT VEGETATION from 1998 to 2012 and combined with harmonic analysis method and linear trend method.【Result】(1) From 1998 to 2012, the start of growing season advanced by 0.9 d on average every year and the end of growing season delayed by about 0.8 d on average every year, the length of growing season every year extended by 1.7 d on average under the joint action of advance at the start of growing season and delay at the end of growing season. (2) Hydrothermal condition on Loess Plateau has an immediate impact on phenological difference, the restrictive temperature for vegetation growth is 9℃，with the restrictive precipitation of 475 mm and 540 mm, respectively and restrictive altitude of 1 750 m. (3) The spatial partial correlation coefficients between the length trend of growing season of vegetation and altitude and air temperature are 0.0591and 0.0139 respectively, the spatial partial correlation coefficients between the length trend of growing season of vegetation and precipitation is -0.0174, therefore, the degree of correlation between three factors and the trend at the start of growing season is higher than that at the end of growing season.【Conclusion】The zones showing a significant and stable trend of phenological feature of vegetation on loess plateau are primarily distributed on plateau in the north of Shaanxi and Beishan in the middle of Shanxi. The phenological change in arid area and desert and grassland area in northwest is mainly subject to control by air temperature. The phenological change in semi-arid area and farming and grassland areas is mainly subject to control by precipitation. The phenological change in agricultural area in Fenwei Basin is subject to hydrothermal condition. Difference in hydrothermal condition has an insignificant impact on vegetation phenology in broad leaved forest zone. Altitude has an insignificant impact on change trend of vegetation phenology on loess plateau. The extension trend of growing season is on the increase with the increase of altitude and air temperature under the joint action of the start and end of growing reason, the shortening trend of growing season is on the increase with the increase of precipitation, the change characteristics of the same type of vegetations in terms of phenological trend based on the change of altitude, precipitation and air temperature are consistent, the change characteristics at the start of growing season have a greater influence on length change of growing season compared with that at the end of growing season.

Key words: vegetation coverage, growth season, harmonic analysis, Fourier interpolation, loess plateau