Abstract: The degradation dynamics of imazapyr in four kinds of soil i.e. powder soil, coast soil, yellow red loam soil and huangjin mud were studied respectively, and the effect of soil-property on degradation was also investigated. The degradation rate constant were 0.022 7,0.023 3,0.017 5 and 0.015 7 respectively in four kinds of soil, among which the fastest occurred in coast soil and the slowest in yellow red soil. The important factors, which influence degradation rate of imazapyr in soil, are organic matter content (OMC) and pH values. Environmental factors also affect imazapyr-degradation rate which will increase as temperature and moisture rise. Temperature effect coefficient(Q) varies from 1.08 to 1.42, which is not in accordance with Van’t Hoff law, and it is proved that the effect of temperature on degradation rate in soil is less than on the decomposition in water. On the contrary, the degradation rate will decrease when the fortified concentration goes up.