The chemical time bomb (CTB) in environmental soil is harshly harmful to ecosystem and human being ourselves. There are numerous bursts of CTB all over the world,but CTB as an environmental hazard is frequently ignored because of its natural of invisibility,which may cause more dangerous catastrophe. It is difficult to discuss the classification of CTB. More attention should be focused on the mechanism and process of CTB formation,which is the basis of assessment and prediction of CTB. It seems that the geochemical engineering technologies will be the most important means for prevention and remediation of CTB. A new concept,delayed geochemical hazard,with broader extension and more profound intension,is suggested to instead the concept of CTB.