The invention relates to a widget application development technique and discloses a three-screen-interaction-based cross-platform widget middleware system. The system comprises a platform migration layer, a core layer and an application layer, wherein the platform migration layer is located at the bottommost layer of a middleware system, is used for packaging functions and APIs (Application Program Interface) of different mobile terminal devices and various mobile operation systems into interfaces to be invoked by an upper layer, and comprises hardware function interfaces of a mobile phone, a set-up box and a tablet personal computer; the core layer is located on the platform migration layer and is used for providing an operating environment for widget application, linking the application layer with the platform migration layer, realizing analysis on xhtml (Extensible Hyper Text Markup Language), xml (Extensive Makeup Language), cascading style sheets, DOM (Document Object Model) and scripting languages and Ajax (Asynchronous JavaScript and XML) interaction functions, and invoking the interfaces of the platform migration layer according to an under-layer instruction; and the application layer is an similar web application located on the core layer and used for providing support for a widget developer to customize and develop corresponding widget applications. The three-screen-interaction-based cross-platform widget middleware system is suitable for developing the widget applications.