Abstract: In the application software development and simulation of water science research， model development and integration technology have become the key research content. As a new method in the model development and integration, OpenMI technology has attracted considerable attention in the field of water environment, and been applied to many projects of international water environment agencies. This paper describes the development of model integration technology and model integration methods commonly used at present. Detailed analysis of the key content of OpenMI by the unified modeling language and in-depth analysis of the connotation of OpenMI technology are carried out. As an example, based on the three-layer evaporation model, OpenMI technology is used to develop soil moisture forecast model with the point of view of software design. A set of practical method is obtained for development and integration in the model. This method not only can be used for the soil moisture forecasting system, but also for much more complex large system areas such as rainfall, runoff and flood forecasting models.