Abstract: This paper describes the three phases involved in the development of an ultimate Earth System Model (ESM), from physical climate system model (the fundamental phase) to Earth climate system model (the transitional phase) and finally to ESM (the prototype phase), based on reviews of existing literature. The authors emphasize the strategic significance for establishing such ESM and introduce some scientific research plans on the development of ESM at home and abroad. They also provide a perspective on the future development of ESM based on current status and trends of the models that participated in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, with the hope to guide future development of ESM in China.