Abstract: The degradation processes of arable Mollisols in Northeast China was studied by soil survey in whole area combined with the data of soil county annals and the Second National Soil Investigation. The results showed the arable Mollisols in Northeast China was seriously degraded after reclamation. Soil organic matter content decreased 60 percent. The soil degradation can be divided into three degradation phases,and the three degradation phases are coexisting. During the twenty years from the Second National Soil Investigation to 2000,the annual decrease in soil organic matter was five thousandth in Mollisols area,and 13.5 thousandth in the counties seriously eroded by water. Therefore soil erosion is the dominant driving factor of the soil degradation. Meanwhile,it was indicated the soil degradation could be prevented or the soil fertility could be improved by increasing the input to field or ecological protection.