A combined grooving blade for synchronous cutting machine with half-closed water cooling channels, wherein the combined grooving blade for synchronous cutting machine with half-closed water cooling channels comprises two outside diamond grooving blades, two internal clamp plates and one central diamond grooving blade, wherein the two internal clamp plates are arranged on both sides of the central diamond grooving blade, and the two outside diamond grooving blades are disposed on outer sides of the two internal clamp plates, the two outside diamond grooving blades, the two internal clamp plates and the central diamond grooving blade are fixed into a hole by fasteners, a plurality of cooling water through holes are uniformly distributed, along the same circumference, on each of the outside diamond grooving blades, cooling water channels are provided on the internal clamp plate and in positions corresponding to the cooling water through holes on the outside diamond grooving blade, the cooling water channels are distributed in the radial direction of the outside diamond grooving blade, the cooling water channels has a graded width, and the width of the cooling water channels close to the center of the outside diamond grooving blade is narrower than the width of the cooling water channels far away from the center of the outside diamond grooving blade, gaps in communication with edges of outer circles of the internal clamp plates are provided on ends of some of the cooling water channels, wherein further - the cooling water channels with the gaps and the cooling water channels without the gaps are spaced on the internal clamp plate, - the number of the cooling water channels arranged on each internal clamp plate corresponds to the number of the cooling water through holes arranged on the outside diamond grooving blade, eight cooling water through holes are uniformly distributed, along the same circumference, on the outside diamond grooving blades, eight cooling water channels are distributed on the internal clamp plate, - the end of the cooling water channels close to the center of the outside diamond grooving blade is in a shape of circular arc, and the end of the cooling water channels far away from the center of the outside diamond grooving blade is in a shape of circular arc, the circular arc at the distal end of cooling water channel communicates with the edges of the outer circles of the internal clamp plates along the radial direction of the internal clamp plates via the gaps, - central holes and positioning holes beside the central holes are provided on the outside diamond grooving blades, the internal clamp plates and the central diamond grooving blade, the sizes and the positions of the central holes and the positioning holes on the outside diamond grooving blade, the internal clamp plates and the central diamond grooving blade correspond with each other, and - the outer diameter of the outside diamond grooving blades is the same as the outer diameter of the central diamond grooving blade, and the outer diameter of the internal clamp plates is smaller than the outer diameter of the outside diamond grooving blades. - the cooling water channels with the gaps and the cooling water channels without the gaps are spaced on the internal clamp plate, - the number of the cooling water channels arranged on each internal clamp plate corresponds to the number of the cooling water through holes arranged on the outside diamond grooving blade, eight cooling water through holes are uniformly distributed, along the same circumference, on the outside diamond grooving blades, eight cooling water channels are distributed on the internal clamp plate, - the end of the cooling water channels close to the center of the outside diamond grooving blade is in a shape of circular arc, and the end of the cooling water channels far away from the center of the outside diamond grooving blade is in a shape of circular arc, the circular arc at the distal end of cooling water channel communicates with the edges of the outer circles of the internal clamp plates along the radial direction of the internal clamp plates via the gaps, - central holes and positioning holes beside the central holes are provided on the outside diamond grooving blades, the internal clamp plates and the central diamond grooving blade, the sizes and the positions of the central holes and the positioning holes on the outside diamond grooving blade, the internal clamp plates and the central diamond grooving blade correspond with each other, and - the outer diameter of the outside diamond grooving blades is the same as the outer diameter of the central diamond grooving blade, and the outer diameter of the internal clamp plates is smaller than the outer diameter of the outside diamond grooving blades.