In order to study the variation law of N_2O emission under different nitrogen fertilization in the rice paddy of Ningxia area, a field experiment was conducted, and in situ observation with static-chamber and gas chromatograph was carried out. The results showed that, the emission of N_2O from rice paddy could be promoted by the nitrogen fertilization, and there were significant differences of the emission of N_2O between rice paddy with different levels of nitrogen fertilization. During the whole observation period, Only one emission peak of N_2O in the rice paddy treated with different nitrogen fertilization was detected at the late stage of rice grain filling, But the emissions of N_2O had no peak in the control treatment and which was mainly at the green, jointing, grain-filling and maturity stage. With the increasing of nitrogen, the loss of nitrogen in the form of N_2O reduced. The N_2O global warming potential (GWP) was increased gradually with the increase of nitrogen amount, and its impact on the environment can not be ignored.