The kinetics of changes in active N (0.05mol/L CaCl₂-extractable Ni) in six different soils was studied in laboratory. Two-constant rate equation,y=ky₀t^1/m,could well describe the changing process of active Ni over time. The parameter k could represent the change rate. The higher the k value, the slower the active Ni changed. The parameter k was negatively correlated with soil pH and CEC, but positively with the transfer coefficient (Tc) of Ni from soil to plant. In addition, the practical application of this equation are discussed as well.