A method and system for cross domain interaction of a Web application are proposed, wherein a Web application belonging to a first domain needs to interact with a service belonging to a second domain. The method comprises: by the Web application, creating an iFrame in a webpage, wherein the iFrame is belonging to the first domain; creating a form in the iFrame; submitting the form to a Web server providing a service belonging to the second domain; and refreshing the iFrame by receiving a response from the Web server, changing the domain, to which the iFrame is belonging, to the second domain, and performing cross domain interaction with the service belonging to the second domain with the information contained in the form.