The application provides a client upgrade method and device, which are applied to a server. The method comprises the following steps: detecting whether an operation control state of an upgraded clienton a virtual machine meets a preset transmission condition; if detecting that the operation control state meets the preset transmission condition, identifying the upgraded client as an available upgrade package; receiving an upgrade request sent by an un-upgraded client; and determining a data providing end for providing an upgrade package transmission service for the un-upgraded client from theserver and the upgraded client identified as the available upgrade package. Thus, in a virtual desktop system that uses peer-to-peer (P2P) transmission for client upgrade, screening is carried out according to the operation control state of the upgraded client on the virtual machine through the server; and the data providing end for providing the update package is determined for the un-upgraded client only in the upgraded client suitable for providing the upgrade package transmission service. Therefore, the upgrade package transmission service can be avoided from impacting the services that the upgraded client is currently using.