Understanding the relationship between the timing of N fertilizer applications and crop primary production is crucial for achieving high yield and N use efficiency in agriculture. This study investigated the effects of starting-N plus topdressing N applications(as compared to the common practice of all basal application) on soybean photosynthetic capacity under different planting densities. A field experiment was conducted in two growing seasons(2011 and 2012), and the soybean(Glycine max L. Merrill) cultivar was Dongnong 52, three planting densities(20, 25 and 30 plants m-2), and four N fertilizer application patterns(all N fertilizer of 6 g N m-2 as basal fertilizer, all N fertilizer as topdressing at beginning pod stage(R3), 1.8 g N m-2 as basal fertilizer and 4.2 g N m-2 as topdressing at stage R3 and full pod stage(R4), respectively). The results indicated that under the same planting density, compared to applying all N as basal fertilizer, the application of starter-N plus topdressing N substantially reduced the rate of pod abscission, and enhanced leaf area index(LAI) significantly at beginning seed stage(R5)(P<0.05), net assimilation rate(NAR) during stages R4-full seed stage(R6)(P<0.05), contribution rate of post-seed filling assimilate to seed(CPA)(P<0.05), and yield(P<0.05). Applying topdressing N at stage R4 resulted in higher net primary production and yield than applying topdressing N at stage R3. When applying starter-N plus topdressing N at planting density of 25 plants m-2, LAI after stage R5 and NAR after stage R4 were increased by 5.92-16.3%(P<0.05) and 13.7-26.6%(P<0.05) with the planting density of 20 plants m-2, respectively, and yield was 8.46-14.0%(P<0.05) higher than that under 20 plants m-2. When planting density increased to 30 plants m-2, only LAI during stages R4-R5 and NAR during stages R4-R5 increased by applying starter-N plus topdressing N, while the other indexes declined. Overall, results of this study demonstrated that applying starter-N plus topdressing N could significantly enhance soybean photosynthetic capacity after stage R5 at planting density of 25 plants m-2. Understanding the relationship between the timing of N fertilizer applications and crop primary production is crucial for achieving high yield and N use efficiency in agriculture. This study investigated the effects of starting-N plus topdressing N applications (as compared to the common practice of all basal application) on soybean photosynthetic capacity under different planting densities. A field experiment was conducted in two growing seasons (2011 and 2012), and the soybean (Glycine max L. Merrill) cultivar was Dongnong 52, three planting densities (20, 25 and 30 plants m-2), and four N fertilizer application patterns (all N fertilizer of 6 g Nm-2 as basal fertilizer, all N fertilizer as topdressing at beginning pod stage (R3), 1.8 g Nm-2 as basal fertilizer and 4.2 g N m-2 as top dressing at stage R3 and full pod stage (R4), respectively). The results indicated that under the same planting density, compared to applying all N as basal fertilizer, the application of starter-N plus topdre ssing N substantial reduced the rate of pod abscission, and enhanced leaf area index (LAI) significantly at beginning seed stage R5 (P <0.05), net assimilation rate (NAR) during stages R4-full seed stage R6 <0.05). Applying topdressing N at stage R4 resulted in higher net primary production and yield than applying topdressing N at (CPA) (P <0.05) stage R3. When applying starter-N plus topdressing N at planting density of 25 plants m-2, LAI after stage R5 and NAR after stage R4 were increased by 5.92-16.3% (P <0.05) and 13.7-26.6% (P < 0.05) with the planting density of 20 plants m-2, respectively, and yield was 8.46-14.0% (P <0.05) higher than that under 20 plants m-2. during stages R4-R5 and NAR during stages R4-R5 increased by applying starter-N plus topdressing N, while the other indexes declined. Overall, results of this study demonstrated that applying starter-N plus topdressing N could significantly enhance soybean photosynthetic capacity after stage R5 at planting density of 25 plants m-2.