Kelly valve is a manually operated ball type drill stem valve; it is divided into upper Kelly valve and lower Kelly valve. The upper Kelly valve is connected between lower end of swivel and upper end of Kelly; the lower Kelly valve is connected between upper end of drill pipe and lower end of Kelly or connected between lower end of Kelly saver subs. The Kelly valve can be opened on or closed off by only turning the special operating wrench at 90° according to indicating direction. During drilling operation, the Kelly valve shall be connected at upper end and lower end of Kelly.