Abstract: A coupled model of photosynthetic rate (Pn) and light use efficiency (LUE) were developed to simulate the three-dimensional distribution of LUE in apple canopy. For convenience, LUE was expressed as the ratio of net Pn to photosynthetically active radiation (PAR). The experiment was conducted in a ‘Fuji’ apple (Malus domestica Borkh. cv. ‘Fuji’) orchard during the 2011-2012 growing seasons. The simulation was shown that: LUE increased rapidly with increasing CO2 concentration and humidity. LUE consistently increased with the increase of PAR when PAR was below 750 μmol/(m2?s). And it decreased with the increase of PAR when PAR excessed 750 μmol/(m2?s). When canopy height increased from bottom to upper canopy, LUE decreased by 50% from 0.02481 mol/mol to 0.01250 mol/mol with no more than 10% difference between the sides and the inner part. The diurnal course of LUE in the canopy showed a double-peak curve on clear day. The average LUE on clear days were 0.01148 mol/mol which were about 22.7% higher than cloudy days. The study indicated that: the sensitivity of LUE to microclimatic factors could be systemically assessed by the coupled model.