The invention discloses a preparation method and medical application of 4-tert-butyl-6-phenyl-2-amino-6H-1,3-thiazine salt. The preparation method of the 4-tert-butyl-6-phenyl-2-amino-6H-1,3-thiazine salt comprises the steps of: stirring 0.010 mol of 1-phenyl-4,4-dimethyl pentene-3-ketone, 0.012 mol of thiourea and 0.011 mol of acid in an organic solvent at a temperature of between 30 and 80 DEG C, performing TLC detection on reaction process, completing reaction, filtering, washing and drying the obtained product and obtaining the 4-tert-butyl-6-phenyl-2-amino-6H-1,3-thiazine salt (I). The 4-tert-butyl-6-phenyl-2-amino-6H-1,3-thiazine salt (I) can be medically used for preparing influenza virus neuraminidase inhibitors. In a formula, HX is hydrochloric acid, phosphoric acid, hydrobromic acid, sulphuric acid, trifluoroacetic acid or methanesulfonic acid, and Y is Cl, Br, CH3, Et, CF3, OCH3 or OEt.