Disclosed are a method and device for implementing instant messaging through a browser. A plug-in interface of an instant messaging tool is preset on the browser. The method comprises: a master process of the browser creating a plug-in process corresponding to the instant messaging tool; triggering the plug-in interface to instruct the master process of the browser to reload a browser window; the master process of the browser dividing, in the browser window, page presentation ranges of a plug-in page of the instant messaging tool and a current tab of the browser window and notifying the plug-in process of the page presentation ranges; and the plug-in process generating the plug-in page according to the divided page presentation ranges and loading the plug-in page and the re-rendered current tab side by side in the browser window.