Decomposition of organic matter is an important and complex process in deformation analysis of wastes. Tests of decomposition and settlement of waste column had been performed under the conditions of nearly unchanged temperature and moisture

zero pressure and bearing water content. During decomposition volume of leach was measured. The behavior of decomposition and its rate was analyzed. Decomposition law including three conclusions was identified. Mathematical expression of the decomposition quantity with time and the method to determine the three parameters in the expression were presented. Calculation result of the decomposition is consistent with the test. The waste column test was simulated by using the decomposition test result. The settlement of the waste column was calculated by considering secondary compression and decomposition separately. It is found that the calculated settlement is in good agreement with the waste column test; and the settlement from decomposition is an more important factor than the secondary compression.