The invention relates to a top-mounted type low-temperature floating ball valve comprising a valve body, a ball body and valve seat assemblies. The ball body is arranged in the valve body. The valve seat assemblies are arranged between the ball body and the valve body. The valve seat assemblies are arranged both on the upstream side and the downstream side of the ball body. Each valve seat assembly comprises a valve seat inner ring, a valve seat and a valve seat support, wherein each valve seat is arranged on the corresponding valve seat inner ring in a sleeved manner, and each valve seat support is connected to the corresponding valve seat in a sleeved manner. According to the top-mounted type low-temperature floating ball valve, the valve seat supports and the valve seat inner rings have a protection function on the valve seats, it is avoided that the valve seats are pressed to deform under the pressure of a medium, the seal reliability of the floating ball valve is improved, and the service life of the floating ball valve is prolonged.