Abstract: A pot experiment was carried out to study the effects of nitrogen fertilization on photosynthetic performances in maize leaves of inbreed line Qi319 (Q319) at grain filling stage using simultaneously analyzing chlorophyll a fluorescence transient and light absorbance at 820 nm. Two years' results indicate that N fertilization had no effect on chlorophyll contents in the ear leaf at grain filling stage, but significantly improved the net photosynthetic rate（Pn） and single plant dry matter and grain yield (Pn and yield was not mainly resulted from the change of chlorophyll content at grain filling stage, but from the enhancement in Q319 photosynthetic performances and improvement of the coordination between PSⅡ and PSⅠand performance of electron transport chain.