Abstract: In order to investigate the characteristic of N fertility and N mineralization in paddy soil of Hunan Province, waterflooded incubation two weeks (improved method) was proposed by Waring and Bremer to study the N mineralization characteristic of three rice based cropping systems paddy soil derived from three kinds of type of parent material in Changsha County, also forecasted the nitrogen supplying capacity of soil. Results showed that, total N and alkaline hydrolytic N of tested soil respectively vary from 0.55-1.50 g/kg and 84.10-182.70 mg/kg, and showed normal distribution. The mineralizable N of tested soil vary from 24.53-84.61 mg/kg, there was significantly positive correlation between the mineralizable N and total N (r=0.467*), and extremely significantly positive correlation between the mineralizable N and alkaline hydrolytic N (r=0.535**). The potentially mineralizable N of tested soil vary from 65.70-170.09 mg/kg, and the mineralization rate constant (c) vary from 0.0083-0.0386. The amount of N supply was forecasted in tested soil was 112.51-422.10 kg/hm2, and the rate of N supply was 7.07%-23.53%. Among three kinds of parent material, the N supply potentiality of tested soil derived from granite weathered material was obviously higher than that of the soil derived from the quaternary red clay and river alluvium; among three based cropping systems, the N supply potentiality in tested soil of rice field transform upland field in 3-5 years was obviously lower than that soil of rice field-upland field rotation and double cropping rice.