This paper provides an overview of model integration in the Digital Heihe River Basin research initiative. ①It could be concluded that model integration plays a backbone role in watershed science. It mainly consists of two themes. One is to develop an integrated watershed model, which should be capable of representing the processes of water-soil-atmosphere-biosphere-human continuum and the interactions among them. The other is to built a modeling environment, which should focus on giving software support for efficient and effective model integration with advanced information and computational techniques. ②It is proposed that the model integration can be implemented in two approaches. The first is defined as the intellective approach, through which the physics of different components of model or module could be completely coupled to form a new model. The second is defined as the technical approach, through which models or modules could be integrated through data exchange interfaces, remaining the core of each model untouched. The importance of the modeling environment to model integration and the relationship between the watershed management model and the scientific model are discussed. ③The overall goal of model integration initiative in the Heihe River Basin is to develop two types of integrated models. One is for scientific purposes, which should be a localization of the Earth system model in the Heihe River Basin and features as a comprehensive model on hydrology, ecology, and economy as well as their interactions at a basin scale. The other is for management purposes, which should target at building a spatially explicit decision support system for integrated river basin water resource management. ④Existing researches on modeling hydrology, groundwater, water resources, land surface processes, land use, ecology, social economics and ecological economics in the Heihe River Basin are summarized. ⑤Bottlenecks in building an integrated model for the Heihe River Basin are addressed.