The invention discloses a loop experimental device for testing gas-dissolved raw oil. Water is circularly pumped between two piston cylinders by utilizing a high-pressure plunger pump, thus driving pistons to move alternatively to drive the gas-dissolved raw oil to flow and ensuring no contact of the plunger pump and the gas-dissolved raw oil; through switching the connection situations among pipelines by two electric four-way valves, injection lines are always connected with the injection lines, output pipelines are always connected with output pipelines, so as to guarantee the flowing unipolarity of fluid, and the pressure of the piston cylinder and loops can be adjusted through two back-pressure valves of the loops; and glass observation pipe segments are arranged on the initial end and the tail end of the loop and used for performing microscope photographing to the particle size and distribution of bubbles on the horizontal, perpendicular longitudinal sections and cross sections of the pipelines, and conducting three-dimension simulation to the flowing state in the pipelines by utilizing weighed reconstruction technology, to obtain the three-dimension flowing state of the fluid. Compared with the existing flowing loop system, the loop experimental device has the characteristics that driving does not need a pump, no shearing exists, the multi-dimensional microscopic of the pipeline flow is visible, the pressure is adjustable, multiple working conditions run, circulating flowing can be conducted, and the loop experimental device can be used in high-temperature and high-pressure environments.