The present invention relates to a compound of a novel antiviral nucleoside reverse transcriptase inhibitor, a pharmaceutical composition comprising the compound, and preparation and application of the compound. Specifically, disclosed in the present invention are a fused pyrimidine compound as represented by formula (I), and a pharmaceutical composition comprising the compound, or a pharmaceutically acceptable salt, stereoisomer, solvate, hydrate, crystal form, prodrug, or isotope derivative of the compound. The compound of the present invention can be used for treatment and/or prevention of infectious diseases caused by viruses, such as human immunodeficiency virus (HIV) and hepatitis B virus (HBV).