Abstract: In order to determine the optimal application rate of nitrogen for the rice restorer line Shuangkang Mingzhan during the seed production, by taking the application rate of nitrogen as the experimental factor, five different application levels of nitrogen were set, and the application rates of urea were set as N1(0 kg·hm^-2), N2(96.30 kg·hm^-2, N3(192.75 kg·hm^-2), N4(289.05 kg·hm^-2) and N5(385.5 kg·hm^-2), respectively, in order to study the effects of different nitrogen application rate on the main agronomic characters of Shuangkang Mingzhan. The results showed that Shuangkang Mingzhan was sensitive to nitrogen fertilizer, and increasing the application of nitrogen fertilizer had obvious effect on increasing the number of productive ear per plant, spikelet number per panicle, spikelet number per plant, thousand seed weight, ear length, the first leaf length from the top, the first leaf width from the top, the second leaf length from the top, the second leaf width from the top, the 3rd leaf length from the top, and the 3rd leaf width from the top. The best fitted equation between the application rate of nitrogen and spikelet number per plant was Y=2 631.168+10.855x-0.030x². According to the best fitted equation, when the application rate of nitrogen was 96.64,265.2kg·hm^-2, the spikelet number per plant was more than 3 400, and the growth period was from 116 to 117 days. So Shuangkang Mingzhan had reasonable population structure, high spikelet number and stable growth period, which was conducive to the seed production and high yield.