In order to work out the laws of piggery wastewater treatment in IC reactor, theoretic kinetics model of substrate decomposing in IC reactor was set up on the basis of analysis for substrate decomposing characteristics in IC reactor, and on the basis of the hypothesis: 1) fluid state in fine treatment section and sludge bed section is flow and plug flow, respectively, 2) the relationship between substrate decomposing and concentration of microbe coincides Class I reaction model. Based on the experimental results, the kinetics parameters of substrate decomposing under the average temperature of (33±0.5)℃ were determined. The validation of the kinetic model shows that most of the errors are no more than 8%, which demonstrates that the kinetics model can provide scientific bases for piggery wastewater treatment by using IC reactor.