LNG (liquefied natural gas) cryogenic ball valve (CBV) is an important flow control device in LNG receiving stations. Its reliability directly affects the stability of the pipeline system, especially its damage or leak in the seat seal will seriously threaten the normal operation and the safety of LNG receiving stations. When LNG flows through the CBV, due to the interaction between fluid pressure and the valve structure, the hard sealing at the valve seat is not only subjected to the pre-tightening force of saucer spring, but also affected by the fluid pressure of the complex flow. Therefore, it is necessary to study the flow characteristics in the CBV and the hard sealing performance affected by the LNG. In this paper, the fluid dynamics and the contact stress on hard sealing performance in the CBV are analyzed. The pressure drop, pressure, and velocity distributions were analyzed, respectively. The contact stress on the hard sealing surfaces of the CBV with fluid pressure was analyzed by the fluid-structure coupling method. This work has a certain reference value for researching and mastering the hard sealing performance of cryogenic ball valves.