The invention provides a tetraterpene compound and a preparation method thereof by extracting from sarcophyton trocheliophrum. The tetraterpene compound provided by the invention has T cell subtype regulation activity, is low in cell toxicity, and can be used for preparing immunomodulatory drugs, antineoplastic drugs or antibacterial drugs. The tetraterpene compound also can be used as a lead compound to open up a new way for developing new drugs.