Conventional geoprocessing workflow tools, such as ArcGIS ModelBuilder, focus on the integration of geoprocessing algorithms. The concept of the "Model Web" brings new challenges to these tools. On one hand, existing geoprocessing tools need to adapt to the Web environment to support the plug-in-and-play of distributed geoprocessing services. On the other hand, these services need to couple complex models to support time-step computation. This paper introduces a new method to publish model as service based on WebSocket protocol, and also introduces a workflow-based integrated modelling approach to couple models and services. It integrates OGC services, WebSocket services and OpenMI models, which brings some new features including logical consistency, physical separation, and controllable execution. In this way, traditional geoprocessing workflow tools are extended as tools for integrated modelling. A specific use case demonstrates the applicability of the approach.