Abstract: ObjectiveIn the present study, effects of different nitrogen application rates on chlorophyll fluorescence characteristics of spring wheat under high temperature after anthesis were investigated , in order to provide guidance for analysis for inner mechanism of nitrogen nutrition regulation of high temperature harm to spring wheat. MethodNingchun 4 and Ningchun 47 were used as plant materials. Three nitrogen application rates, 120 kg/ha(N1), 240 kg/ha (N2) and 300 kg/ha(N3), were set and no nitrogen application was treated as control(CK). High temperature treatment during 18-22 d after anthesis on wheat was conducted. Chlorophyll content and fluorescence parameters were measured 7 , 14, 23, 28 and 33 d after anthesis. ResultUnder high temperature stress(23-33 d after anthesis), SPAD values, maxi-mum fluorescence(Fm) and variable fluorescence(Fv) in leaves of Ningchun 4 and Ningchun 47 under three nitrogen app-lication rates increased, but original fluorescence(Fo) declined, which rose Fv/Fo and Fv/Fm and decreased Fo/Fm. The variation ranges of wheats in N1 and N2 treatment were larger than the one in N3 treatment compared with CK. Ab-sorption flux per RC (ABS/RC) , trapped energy flux per RC (TR0/RC) and dissipated energy flux per RC (DI0/RC) in N1 and N2 treatments were significantly higher than those of CK during 23-28 d after anthesis (P<0.05,the same below), and significantly lower than those of CK on day 33 after anthesis. Electron transport flux per RC (ET0/RC) was expressed as N2>N1>N3>CK during 23-33 d after anthesis. ConclusionAppropriate application of nitrogen fertilizer can alleviate the damages to structure and function of spring wheat photosynthetic organ caused by high temperature , and improve pho-tosynthetic performance.