Abstract: An anomaly model is derived under the two independent presuppositions that are the annual climate is the solution to the equations controlling the climate system evolvement and the basic quantity of annual climate is much Larger than the perturbation quantity of the annual climate disturbance. The first presupposition relaues the conditions of the anomaly model and in the second presupposition the anomaly model is approximately existent. In addition, we find that the observational annual climate used in the anomaly model corresponds to the modification of the annual climate used in the non-anomaly model.