Soil moisture is one of the main limiting factors in vegetation survival.The objective of this study is to provide a theoretical basis for vegetation restoration in semi-arid valley area in Lhasa by studying environmental factors that affected soil moisture.In this study,three land types(flood land,terrace and footslope)including 7 typical forestland sites were selected.In field investigation,a survey of 10 environmental factors that were classified into soil properties,topography and geomorphology,and vegetation types,was conducted.The major factors affecting soil moisture and relationship among factors were analyzed with correlation analysis and principal component analysis.The results showed that the relationships between soil moisture and environmental factors were inconsistent among 3 different land types,whereas the same relationship was found between flood land and terrace.There was a non-significant positive or negative correlation between soil moisture and environmental factors.However,significant positive correlations were found among environmental factors.In footslope area,the soil moisture was significantly related to the environmental factors,and the correlation between environmental factors was significant as well.The key factor affecting the soil moisture in flood land and terrace was soil properties first,followed by vegetation types.The strongest factors affecting soil moisture in footslope area were topography and geomorphology,and the vegetation type was next.The soil properties had the weakest influence.Soil moisture was the result of the effects of a number of environmental factors.For each land type,the principal components were definite,which had a clearly explanation for soil moisture.The topography,vegetation and soil type were major factors that affected soil moisture in semi-arid valley of Lhasa.