Abstract: A method, device, and data download system for controlling effectiveness of a download transaction. The method includes: resolving, by a download server, a transaction ID generation request from a download portal, dynamically generating a transaction ID according to a current download transaction and sending the transaction ID to the download portal; sending, by the download portal, a download address corresponding to a download content selected by a download client and the transaction ID to the download client; the download client redirecting to the download server according to the download address, and sending a download request containing the transaction ID; and authenticating an identity of the download client and verifying the transaction ID by the download server, if the verification is passed, transferring, by the download server, the corresponding download content to the download client; otherwise, the download fails.