Using the NDVI ratio method, the authors extracted phenological parameters from NOAA-AVHRR NDVI time-series data (1982–2008). The start of the growing season (SOS) and the date of maximum NDVI (Peak-t) correlated significantly with the mean annual precipitation along regional gradients of the steppes. Along the south transect (located at a lower latitude with a higher annual mean temperature) there was a positive correlation between the end of the growing season (EOS) and the mean annual precipitation along precipitation gradients (R2 = 0.709, p < 0.0001). However, along the north transect (located at higher latitude with lower annual mean temperature), the EOS was slightly negatively related with the mean annual precipitation (R2 = 0.179, p < 0.1). There was positive correlation between the length of the growing season and the annual precipitation along two transects (R2 = 0.876, p < 0.0001 for the south transect; R2 = 0.290, p < 0.01 for the north transect). Thus, for the Inner Mongolian steppe, it is precipitation rather than temperature that determines the date of the SOS.已有的物候研究主要针对温度的影响，而降水量的物候效应研究相对较少。文中用NDVI比率法分析内蒙古草原两个同温样带的年降水量与草原物候之间的关系。结果表明，在中国温带草原区，年降雨量增加能显著促进春季植物的萌芽和夏季最高生物量日期的到来，而年平均温度起抑制的作用。在低纬度的同温样带（内蒙古中部草原），年降水量增加能延迟生长期结束日期，而在高纬度地区（呼伦贝尔草原）年降水量增加会轻微提前结束生长期。因此在内蒙古中部草原年降水量增加能明显延长草原植被的生长期。