Plant architecture is an important determinant of crop performance and agro-ecological adaptation. In this study, a field experiment was carried out during the 2008-2009 season to study the architecture of two winter wheat cultivars in situ with a 3-D digitizer at the grain filling stage. The parameters describing plant architecture were analyzed and 3-D light capture and potential carbon gain of the plant were calculated. Simulation results showed that light capture and potential carbon gain were more uniformly distributed for the cultivar with more erect leaves. At the grain filling stage, the photosynthetic contributions were about 55%, 49% and 30% for flag leaf, ear, and stem relative to total leaf photosynthesis.