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The aboveground biomass and yield of winter wheat depend on intercepted photosynthetically active radiation (PAR) by crop canopy and radiation use efficiency (RUE). At present, many successful crop growth models estimate aboveground biomass accumulation and yield formation based on fraction of intercepted PAR (FIPAR) and RUE. In order to investigate the influences of water stress on FIPAR and RUE of winter wheat at different growth stages, field experiments of winter wheat were conducted under a rainout shelter in two growing seasons (2015—2016 and 2016—2017) in Yangling, Shaanxi Province. The experimental design involved four different treatments of water stress: no irrigation at greening and jointing stages (namely the early stress, ES), no irrigation at heading and filling stages (namely the later stress, LS), no irrigation at all stages (namely whole stress, WS), and full irrigation at all stages (namely CK). The irrigation level was 80mm. The incident solar radiation by the canopy was continuously measured all day with PAR sensors installed at the center of each plot. The results showed that the relative available soil water content can effectively reflect water status of winter wheat under different drought treatments. The maximum leaf area index (LAI) of ES, LS and WS were 31%, 15% and 58% lower than that of CK treatment, respectively. Affected by LAI, the maximum FIPAR of CK, ES, LS and WS were 90%, 88%, 79% and 42%, respectively. And the WS treatment was significantly lower than the other three treatments for the maximum FIPAR. Meanwhile, the difference of LAI and FIPAR among different treatments resulted in different extinction coefficient, especially the extinction coefficient of ES is lower than that of LS. The averaged aboveground biomass of CK, ES, LS and WS treatments across the two growing seasons were 1532g/m2, 1410g/m2, 1403g/m2 and 537g/m2, respectively. For RUE of winter wheat, the CK treatment was 355g/MJ, and the ES and LS treatments were 22% and 5% lower than the CK treatment, in addition, the WS treatment was 22% lower than CK. The RUE of winter wheat was firstly increased and then decreased through whole development season, and peaked at the flowering stage. The RUE reduction of winter wheat caused by water stress in the vegetative stage was greater than that in the reproductive stage under water stress. The RUE of winter wheat under the WS treatment showed very different responding mechanisms to water stress, which needed further study. The research result suggested that if the extinction coefficient and RUE that can be treated as a function of growth stage or thermal time accumulated temperature rather than a single constant, the estimation accuracy of dry matter in the current model could be improved and the uncertainties of the model could be reduced under serious water stress. 