The present invention relates to an active defense method based on cloud security comprising: a client collecting and sending a program behavior launched by a program thereon and/or a program feature of the program launching the program behavior to a server; with respect to the program feature and/or the program behavior sent by the client, the server performing an analysis and comparison in its database, making a determination on the program based on the comparison result, and feeding back to the client; based on the feedback determination result, the client deciding whether to intercept the program behavior, terminate execution of the program and/or clean up the program, and restore the system environment. The invention introduces a cloud security architecture, and employs a behavior feature based on active defense to search and kill a malicious program, thereby ensuring network security.