The invention relates to a method and system for upgrading a client application program. The method includes the steps that after an application icon of a client is clicked, whether the application program of the client has the latest version is judged, and if yes, an upgrade server address list is obtained; according to the upgrade server address list, an upgrade server address which can be connected is selected, wherein the connected load number does not exceed a preset value; the upgrade server address is accessed, xml configuration information of the latest version is obtained, and an upgrade file is downloaded, wherein the xml configuration information includes a first MD5 value, and the upgrade file includes a second MD5 value; whether the first MD5 value is consistent with the second MD5 value is judged by comparison, and if yes, according to the upgrade file, the application program is upgraded. By means of uniqueness of the MD5 values, the accuracy of file upgrading is guaranteed, at the same time, after the application icon is clicked, whether there is the latest version is judged, according to the load balancing principle, the upgrade server address is selected, forced upgrading is conducted under certain conditions, and the problem that software upgrading is slow is solved.