The invention discloses a milling method used for machining a blade root groove, and relates to a blade root groove milling method. The problem that an existing blade root groove machining manner is large in cutting allowance, extremely low in machining efficiency and prone to knife colliding is solved. The method comprises the steps of blade root groove rough milling, specifically, the blade rootgroove is roughly milled through adoption of spiral line cycloid small cutting depth feeding machining manner, the spiral feeding step is controlled to 1 mm, the rotating speed is 3000 r/min, the feeding amount is 1500 mm/min, the cutting depth is 10.3 mm; when the blade root groove is roughly milled, 0.2 mm allowance is reserved on the groove bottom, and the 0.3 mm allowance is reserved on the two side walls of the groove; blade root groove finish milling, specifically, during blade root groove finish milling, the machining manner that the two side walls of the blade root groove are milled is adopted, one side of the two side walls of the blade root groove is milled, and then the other side wall of the two side walls of the blade root groove is milled; and according to the cutting parameters, the rotating speed is 3000 r/min, the feeding amount is 800 mm/min, and the cutting depth is 0.2 mm. The method is used for machining the blade root groove.