To provide a work method for removing a valve with a pipe and its jig capable of removing and mounting the valve connected to the pipe even during operation.

In a method for removing a valve 12 connected between a flange 14a of a tank side pipe 11a connected to a tank 10 and a flange 14b of a usage side pipe 11b during operation, the flange 13a on the tank side of the valve 12 is covered with half cylinders 16, 17 so as to cover the tank side pipe 11a and a storage 19 is formed in the half cut cylinder 17 to previously store a seal device 18. The flange 13a of the valve 12 is lifted up from the flange 14a of the tank side pipe 11a to move the seal device 18 to the tank side pipe 11a through between the flanges 13a, 14a and fit and seal the tank side pipe 11a with the seal device 18 for removing the half cut cylinders 16, 17 as well as the valve 12.