The invention discloses a method for curve surface grinding with a cylindrical grinding wheel at a virtual ball cutter radius. The method includes the steps that 1, the attitude angle of the cylindrical grinding wheel is designed, and the inclination angle of the axis of the cylindrical grinding wheel on a curve surface tangency point normal vector is designed through a virtual ball cutter model; 2, a cutter path is planned and determined according to the curved surface tangency point normal vector and the virtual ball cutter model, and the set inclination angle in the step 1 is guaranteed through a rotating shaft of a machine tool; 3, by the adoption of an axial feeding mode, a workpiece is subjected to grinding machining according to the cutter path. The cylindrical or quasi-cylindrical grinding wheel can be used for four-axis machining of a free curved surface, and the method has the advantages that planning of the cutter path is simple and flexible, the precision of a machining shape is high, and surface roughness is low, and is suitable for machining free curve surfaces of optical glass and other hard brittle materials.