The invention relates to a triazine compound with a structure represented by a formula A, or a stereoisomer, a prodrug, an active metabolite or a pharmaceutically acceptable salt, a solvate or a crystal form thereof, a pharmaceutical composition of the triazine compound, the stereoisomer, the prodrug, the active metabolite or the pharmaceutically acceptable salt, the solvate or the crystal form, and a use method of the triazine compound. In addition, the invention also relates to a method for preparing a 3C-like cysteine protease inhibitor or a medicine for treating and / or preventing virus infectious diseases. In particular, the present invention relates to the use for treating viral infectious diseases such as Middle East Syndrome Related Coronavirus (MERS-CoV), Severe Acute Respiratory Syndrome Related Coronavirus (SARS-CoV), Influenza A virus, Influenza B virus, Novel Coronavirus Pneumonia (COVID-19) and the like.