The 15N isotope dilution method was used in a short-term (7 days) incubation experiment to quantify gross nitrogen transformation rates of three layers of 0-20cm, 20-60cm and 60-90cm in a paddy soil. The results indicated that, 2h after the addition of 15N solution, the gross mineralization, nitrification and immobilization rates of all layers were significantly higher than other time periods (p<0.01). After 2h, the mineralization rates were fluctuant within a small range. Nitrification rate of 0-20cm layer decreased significantly with time, however, the rate of other two layers changed little. According to the statistical analysis, the changes of the nitrification rates were positively correlated with the changes of soil NH4+-N content. Besides, it is worth to notice that 2h after the addition of 15N solution, a large amount of NH4+-N and NO3--N were immobilized, and it might be mainly contributed to abiotic immobilization. Furthermore, the turnover between immobilization and re-mineralization happened in the 7 days incubation experiment. The results showed that gross nitrogen transformation rate was more useful to quantitatively describe a single nitrogen transform process compared with net rate, but for the reason of irritant effort of the addition of 15N solution, re-mineralization, and the neglect of gas loss, as well as DNRA (Dissimilatory nitrate reduction to ammonium) in this research, there was a difference between the true transformation rates and the estimated ones.