The utility model relates to a top mounted ball valve that on -line maintenance can dismantle fast. Mainly solve current top mounted ball valve and dismantled awkward problem on line. The valve body is equipped with disk seat hole I, disk seat hole II and disk seat hole III, and disk seat, thrust bearing and fixing base have been put into respectively to disk seat hole I, disk seat hole II and disk seat hole III, and fixed connection between thrust bearing and the disk seat, thrust bearing are equipped with the spring hole and at the spring hole cylinder elastic component of packing into, it is the pressure chamber that fixing base, disk seat, thrust bearing, disk seat hole I and disk seat hole II have formed an inclosed chamber, is equipped with through -hole and interface intercommunication on the valve body of pressure chamber upper portion, the ready -packaged joint is installed to the kneck. On the reasonable reliable and simple of this top mounted ball valve that on -line maintenance can dismantle fast structural design, pressure joint arrange the valve body in, the stable performance, the practicality is strong.