The combined application of chemical fertilizers and organic fertilizers in farmland promotes the recycling of organic waste, and has also effects on improving soil properties and increasing nutrient utilization efficiency. In this study, a field experiment with four treatments, that is no nitrogen fertilizer (N0), half of the nitrogen fertilizer (1/2N), 100% of the nitrogen fertilizer (N) and pig manure substituting 50% of the chemical nitrogen fertilizer (1/2N+M), was conducted to explore the effects of combined application of chemical fertilizers and pig manure on soil nitrogen contents and nitrogen use efficiency (NUE) in the double rice cropping system in Changsha county, Hunan Province, so as to provide theoretical support for reducing the application of chemical fertilizers. The soil total nitrogen (STN), available nitrogen (NH4+-N and NO3--N), microbial biomass nitrogen (SMBN), rice yield and rice nitrogen contents were measured in four rice seasons in the 5 and 6 years after the beginning of the field experiment. The results showed that STN increased significantly by 19% in the 1/2N+M treatment as compared with the N treatment, while STN decreased significantly by 20% in the N0 treatment. Soil NH4+-N contents significantly increased in the late rice season in the 1/2N+M treatment as compared with the N treatment. Rice nitrogen uptake was mainly positively correlated with nitrogen application rate, STN, soil NH4+-N and SMBN contents. In the two-year experiment, the rice nitrogen uptake and NUE in the late rice season for the 1/2N+M treatment increased significantly by 9.2%~18.0% and 19.6%~43.0%, respectively, as compared with the N treatment. However, there were no significant increase or decrease of these parameters in the early rice season. This study indicates that combined application of chemical fertilizers and pig manure can increase soil nitrogen availability, reducing chemical fertilizers application, and increasing nitrogen fertilizer use efficiency in the late rice season in the double rice cropping system.