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Increased nitrogen (N) application has profound effects on CO₂ flux in croplands. The aim of this study is to investigate the effects of long-term N addition on soil respiration (SR) in a rainfed winter wheat (<i>Triticum aestivum</i> L.) field in the Loess Plateau of China. Two wheat cultivars were planted under three levels of N application (0, 180, and 360 kg N ha⁻¹ year⁻¹) in non-irrigated cropland from 2004 to 2013. The diurnal and seasonal SR variations and abiotic and biotic factors were measured during the growing seasons in 2012–2013. The results showed that N₁₈₀ and N₃₆₀ increased the cumulative CO₂ flux by 30.3% and 32.4% on average after 5 and 10 years of N application, respectively. Multiple regressions revealed that the seasonal SR was mainly controlled by the soil temperature (ST), at a depth of 8 cm, and the leaf area index. Diurnal SR was mainly controlled by the ST and the net photosynthesis rate. Long-term N application stimulated SR by increasing the photosynthetic leaf area and temperature sensitivity. Overall, N application at a rate of 360 kg N ha⁻¹ year⁻¹ did not reach the threshold for limiting SR in the investigated semi-humid rainfed wheat cropland in the Loess Plateau of China.