The invention discloses an experiment device and an experiment method for representation of the diffusion pressure micromechanism in the grouting process, the experiment device comprises experiment tubes, wherein the experiment tubes are filled with filling media with different particle diameters in sections, one ends of the experiment tubes are communicated with a grouting equipment system by a grouting pipeline, and the other ends of the experiment tubes are connected with a leachate collection cup by a guide tube; test points are arranged in the positions, where the filling media with different particle diameters are located, of the experiment tubes respectively, and sampling tubes which can be opened are arranged at the test points and used for sampling the filling media in the experiment tubes to test the porosity; tees are arranged at the test points in a communication manner, one ends of the tees are communicated with the cavities of the experiment tubes, pressure sensors are arranged at one ends of the tees, and the one end of the tee is connected to a section leachate collection cup by a collection valve. The experiment device and the experiment method study the pressure change micromechanism in the multi-pore medium diffusion process through controlling the grouting parameters (grouting pressure, slurry viscosity and grouting time) and measuring the characteristics ofthe leachate, the porosity of the filling media and the diffusion pressure of all test points.