To provide the manufacturing method of a flange type ball valve seat which can reduce a material cost and shorten a manufacturing time and hold the strength of a forged main body.

The proper position of each neck is divided by making the outer look of a general flange type ball valve to a base. In the case of two flanges type ball valve seat, four parts such as a water take in seat 1, a ball valve seat 2, a limit seat 3 and a water take out seat 4 are formed by forging. In two flanges type valve, the water take in seat 1 and ball valve seat 2, the limit seat 3 and water take out seat 4 are welded respectively so as to make right/left main bodies. Center through holes 112, 222, 312, 412 can be formed by forging together.