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In order to study the characteristics of sunflower canopy development and its absorption and use of radiation in saline fields, two years of field experiments were conducted in Hetao Irrigation District of Inner Mongolia in 2015 and 2016. Three salinity levels were set according to the average ECe of 0~60cm depth: mild (S0: 0~3dS/m), moderate (S1: 3~6dS/m) and severe (S2: >6dS/m); the 〖JP2〗nitrogen application rates were set at four levels, referred as N0, N1, N2 and N3, which were 45kg/hm2, 90kg/hm2, 135kg/hm2 and 180kg/hm2, respectively. The dynamics of LAI, extinction coefficient, light interception and radiation use efficiency (RUE) of sunflower were measured under different salinity and nitrogen levels. The results showed that salt stress obviously inhibited the increase of CLAI at seedling and bud stages, and its effect were more severe under N3 treatment, which decreased the CLAI at S1 and S2 levels by 48.3% and 64.6%, respectively, compared with S0. However, the effect of S1 level on canopy development could be alleviated before the end of vegetative growth, whereas the compensatory growth of sunflower occurred after entering mature stage at S2 level. The daily fraction of light interception (fPAR) and RUE of each treatment were increased constantly from seedling to bud stage, and reached the peak value in flowering stage, and then decreased in mature stage. Among them, the fPAR and the cumulative intercepted PAR of S0N3 treatment were higher than those of the other treatments during the crop cycle, but the maximum RUE appeared in S1N3, which reached 2.26g/MJ in the same year. The research result also slowed that the extinction coefficient of sunflower in this experiment was 0.729. By combining the modified Logistic equation with the linear correlation between LAImax and the effective nitrogen application rate (ENA), a model describing the dynamics of LAI with normalized developmental index under different salinity and nitrogen levels was established. These results proved that applying N2 and N3 rate at S1 level could alleviate salt stress, promote leaf growth and light interception, and increase RUE and seed yield accumulation. However, at S2 level, the N2 and N3 rate had no benefit on canopy development and yield accumulation, but could even reduce the RUE before mature stage. The conclusion helped determining the reasonable rates of nitrogen fertilizer under different saline conditions.