Downhole isolating valve

The utility model relates to an oil field drill completing tools, in particular to a downhole isolating valve. The inner wall of an outer pipe of the downhole isolating valve is in threaded connection with a runner pipe, and the inner wall of the outer pipe is sealed with the runner pipe through a sealing ring. A ball seat is connected on the inner wall of the runner pipe through a shearing pin. The ball seat is correspondingly communicated with a running hole in the runner pipe. Sealing rings are arranged on the upper portion and the lower portion of communication holes of the ball seat so that the ball seat and the runner pipe can be sealed. An anti-toppling ring is arranged on a step of the ball seat and is locked through an anti-toppling ring blocking sleeve. A ball seat blocking sleeve and the lower end of the runner pipe are in threaded connection and are fixed through an anti-rotating pin. A runner lower connector and the lower end of the outer pipe are in threaded connection and are fixed through an anti-rotating pin. According to the downhole isolating valve, a self-locking function is achieved, reliability of isolation is improved, and annular fluid reverse is avoided, and the shortcomings that an existing isolating valve is not reliable in isolating, and annular fluid reverse can happen easily are overcome.