The invention discloses a ball-head cuter processing shaft vector smoothing method based on a BA type five-axis numerically-controlled machine tool. The method comprises: a relation equation between a ball-head cuter shaft vector and a cutter spacing design variable is established; a motion transformational equation between the ball-head cuter shaft vector and drive shafts B and A of a five-axis numerically-controlled machine tool is established; a relation equation between a ball-head cuter spacing design variable and drive shafts B and A of the five-axis numerically-controlled machine tool is established; a design variable, an objective function and a constraint condition of ball-head cuter shaft vector smoothing are determined and a BA-type-five-axis-numerically-controlled-machine-tool-based ball-head cuter processing shaft vector smoothing mathematical model is established; and a solution method of the shaft vector smoothing mathematical model is determined. With the method disclosed by the invention, the rapid change of the drive shaft of the machine tool can be avoided and thus the drive shaft of the machine tool can work smoothly and stably, so that the angular velocity and the angular acceleration speed of the drive shaft of the machine tool can be reduced and thus the processing quality and the processing efficiency of the curved surface can be improved. The method has the high practical application value.