The present invention relates to a valve sealing system (180) in a ball valve wherein a hollow ball (110) is inserted into a ball housing of a valve and the ball (110) rotates with the operation of a handle consisting a flange (150) and a stem (170) to open or close a flow passage. The valve sealing system (180) comprises: an O-ring (182) installed on a first groove (181) to primarily prevent fluid leakage between the stem (170) and a stem cover (172); and a refractory sealing member (184) installed on a second groove (183) to secondarily prevent fluid leakage from the O-ring (182). The valve sealing system is characterized by having a flow passage (185) between the first groove (181) and the second groove (183) to allow the leaked fluid to flow from the O-ring (182), and a pressing means (186) installed on the second groove (182) to prevent the leakage of the fluid leaked from the O-ring (182) by delivering the pressure by the fluid introduced through the flow passage (185) to the refractory sealing member (184). According to the present invention, the valve sealing system can effectively seal a space between the stem and the stem cover even in case the O-ring is not able to seal the space.
