[Objective] The aim of the research was to prove up the effects of N fertilizer on the growth and development of sweet sorghum.[Method] With Chuntian 2 as tested materials,5 treatments of nitrogen fertilizer rate were set up to study the effects of N application rate on the photosynthetic characteristics,sugar accumulation and yield of sweet sorghum.[Result] The photosynthesis of sweet sorghum showed a strengthening trend with the increasing of nitrogen rate in jointing stage.After the jointing stage,the ph...