Abstract: To reveal the changing trends of light use efficiency of kiwifruit orchards at different scales in the humid regions of Southwest China and to explore the influence mechanism of physiological, environmental and vegetation factors on light use efficiency of kiwifruit orchards at different scales. The vorticity correlation system was used to conduct comprehensive observations of water, heat and carbon flux for three consecutive years from 2018 to 2020 in the kiwifruit orchards in Pujiang County, Sichuan Province. The regulations of light use efficiency at different scales in kiwifruit orchards were explored. The path analysis method was used to quantify the total effect of physiological factors, climatic factors, soil moisture factors, and vegetation factors on the light use efficiency of kiwifruit orchards at different scales. The results show that kiwifruit′s leaf instantaneous light use efficiency（LUE_i） decreases with increasing photosynthetically active radiation（PAR）, ranging from 0.006 to 0.026 μmol/μmol. The monthly average daily changes of canopy light use efficiency（cLUE） and ecosystem light use efficiency（eLUE） are U-shaped. The monthly cumulative cLUE and eLUE range between 0.77-2.67 and 0.58-1.63 g/MJ, respectively, and their trends are the same with no obvious seasonal change. LUE_i is mainly affected by meteorological factors（PAR） and physiological factors（P_n） significantly, and PAR and P_n have significant direct（-0.99） and indirect（-0.81） effects on LUE_i, respectively; cLUE and eLUE are significantly affect by meteorological factors（R_g, T_a and VPD） and vegetation factor（LAI）. R_g and VPD mainly affect eLUE and cLUE by affecting the light absorption process, while T_a and LAI affect eLUE and cLUE through carbon assimilation.