[Background]Climate change and human activity lead to vegetation cover obviously changed in the Yellow River basin.Thus,it is necessary to study the temporal and spatial variation of vegetation change from multiple time scales.This paper aims to understand which one of trends with different time scales may represent the changing trend of vegetation in Yellow River basin.[Methods]Two processed datasets of NDVIs,GIMMS and MODIS in Huayuankou Hydrologic Station were used for this study,because the lower reaches of the Yellow River after Huayuankou has a small area and mainly are cultivated land,the data in Huayuankou Hydrologic Station should enough represent NDVI changes in the Yellow River basin.Firstly,linear fitting was applied to calibrate the spatial distributions of NDVI in the Yellow River basin at different temporal scales.Then,Mann-Kendall trend analyzing method was adopted to detect the trends of NDVI with different time scales.Finally,matrix was used to analyze the correlations of NDVI trends between different temporal scales.[Results] 1) The general spatial distribution characteristics of NDVI was low in the northwest and high in the southeast of the Yellow River basin,and NDVI increased gradually from northwest to southeast.The spatial distributions of NDVI in summer and autumn were similar,as well as the same in winter and spring.2) More than half area with increasing trend of NDVI was detected on yearly scale in the Yellow River basin from 1982 to 2012.As for seasonal scale,some areas had increasing trend of NDVI in winter and spring,while less area had increasing tread of NDVIs in summer and autumn.Area with increasing trend in March and October was more than in other months.3) The performance of annual trend was combination of multiple months,while the performance of seasonal trend was contributed by single month.Increasing trend of NDVI in winter was mainly contributed by increased vegetation cover in February,but increased vegetation cover in October failed to make an obviously increasing trend of NDVI in autumn.[Conclusions]The change of vegetation cover has obvious differentiation at different time scales in the Yellow River basin.The increasing trend of NDVI with yearly scale is not necessary available for all the seasons,and months with increasing trend of NDVI are mainly March and October.In total,the results of NDVI trend analysis in annual scale do not fully represent trends of other time scales.Not only the trend of yearly scale,but also the seasonal scale and monthly scale should be calculated and verified for analyzing the trend of NDVI with yearly scale.