The invention discloses a pipe fitting blocking device of a fluid pipeline. The pipe fitting blocking device of the fluid pipeline is used for blocking a flange blocking seat on a pipe fitting. The pipe fitting blocking device of the fluid pipeline comprises a blocking plate, a seal groove for mounting a seal ring is formed in the outer circumference surface of the lower side of the blocking plate, a rotating plate groove is formed in the center of the top of the blocking plate, a plurality of inserting plate grooves are uniformly formed in the circumference direction of the rotating plate groove, a rotating plate is arranged in the rotating plate groove, an inner screw hole joint is mounted on top surface of the rotating plate, inserting plates are slidably mounted in the inserting plate grooves, the rotating plate is connected with the inserting plates through shifting forks, one end of each shifting fork is hinged to the top surface of the rotating plate, other ends of the shifting forks are hinged to top surfaces of the inserting plates, the rotating plate drives the inserting plates to slide in the inserting plate grooves through the shifting forks, pressing plates for preventing the inserting plates from dropping are disposed on the blocking plate, and two sides of the pressing plates press upper side edges of two sides of the inserting plates. According to the pipe fitting blocking device of the fluid pipeline, pipeline blocking from inside to outside can be achieved, process and labor for punching in the blocking seat can be omitted, dangers of gas leakage from screw holes can be avoided, and safety and reliability can be further achieved by the aid of blocking from inside.