The invention discloses a 2,3,5,6-tetrasubstituted-3H-1,2,4-triazine derivative and a synthesis method thereof. Alpha-carbonylenamine and a diazonium salt are taken as starting materials for constructing two C-N bonds in one the step through substitution and cyclization reaction under alkaline conditions in the presence of a copper salt as a catalyst to generate the 2,3,5,6-tetrasubstituted-3H-1,2,4-triazine derivative, and the obtained triazine derivatives have certain potential drug activity. The method has the advantages of easily available raw materials, simple and convenient operation, mild synthesis reaction conditions, high reaction efficiency and diversity of functional groups.