Provided are a phthalazinone compound, method for preparation thereof, pharmaceutical composition thereof, and a use thereof; the structure of said phthalazinone compound is as represented by formula I; the compound of said formula I is targeted to a viral nucleocapsid; it can inhibit the replication of a virus by means of interference of the viral nucleocapsid, has a potent activity for inhibiting HBV DNA replication and a good liver targeting, can stably exist and enrich in the liver, and is a new and effective anti-HBV inhibitor.