The invention discloses a long distance slurry pipeline transportation pressure detection system and a detection method thereof, the detection system includes a detection ring pipe, a micro-differential pressure transmitter and a mercury U-shaped pipe differential pressure gauge, the detection ring pipe and a main pipe are completely same and are arranged in parallel, the micro-differential pressure transmitter and the mercury U-shaped pipe differential pressure gauge are arranged at two ends of the detection ring pipe, a main pipe valve is arranged in the main pipe, a ring-shaped inlet valveis arranged at an inlet end of the detection ring pipe, and a ring-shaped outlet valve is arranged at an outlet end. The micro-differential pressure transmitter detects pressure difference of two ends of the ring pipe, and sends the detected differential pressure value to a programmable logic controller; and a pipeline operation expert system obtains the differential pressure value from the programmable logic controller and calculates frictional resistance of unit length under current flow velocity and concentration by combining with actual length of the detection ring pipe. The system disclosed by the present invention solves problem of large error of theoretical calculated value and actual value when two-phase flow is in turbulence state, and guarantee that the long distance slurry pipeline operation is safe, stable and high efficient.