Abstract: The disclosure provides a login method, an open platform identification method, an open platform and an open platform system. A user terminal is guided to agree to authorize a third party application via a page of the open platform; when the connection of authorization of the user terminal succeeds, the open platform brings a first OpenID and a first OpenKey of the user to the third party application according to a login rebound protocol of the open platform; then the third party application performs user-terminal-based authorized login according to the first OpenID and the first OpenKey; and when the user terminal logging into the open platform initiates the third party application, a prompt message is sent to the user terminal with an open platform account serving as an identification of the open platform, and thus login can be implemented in various forms.