The invention relates to a free floating-ball type drain valve. The drain valve comprises a valve body, a valve cover, a floating ball, a filtering net, a valve seat and a valve seat cover, wherein the valve body is provided with a water inlet and a water outlet; the top of the valve body is provided with the valve cover; the floating ball and the filtering net are arranged in the valve body; the filtering net is arranged above the floating ball; the valve seat is arranged on the lateral lower part in the valve body and fixed through threaded connection; the top end of the valve seat points to the floating ball and contacts with the surface of the floating ball to form a sealing surface; the valve seat cover is arranged on the surface of the valve body; and the valve seat is sealed in the valve seat cover. Compared with the prior art, the free floating-ball type drain valve has the advantages of simple structure, simpler manufacturing process, fast assembly, shorter product manufacturing time and lower manufacturing cost; meanwhile, through the technological improvement of adding a gravity center positioning mechanism in the floating ball, a welding line is protected against impact and the service life of the product is greatly prolonged.