The invention provides a data on-line migration method and device for updating applications in a network platform in order to solve the problem that services fail to be executed in the prior art. The method includes the steps that at the first stage of updating, a new version application and an old version application are run simultaneously, and the new version application and the old version application have access to an old database in the running process; the first stage of updating is finished, data in the old database are all synchronized to a new database, the second stage of updating is carried out, the new version application and the old version application are run simultaneously, the new version application has access to the new database in the running process, and the old version application has access to the old database; the second stage of updating is finished, the third step stage of updating is carried out, the new version application and the old version application are run simultaneously, and the new version application and the old version application have access to the new database in the running process; when the third stage of updating is finished, the new version application is run, and the new version application has access to the new database in the running process.