The invention discloses a hydrodynamic grouting test device simulating different filler gaps and belongs to the technical field of geotechnical engineering. The device is based on the research of the bentonite slurry diffusion rule in sandy soil filled gaps and experimental study on grouting and water plugging effects under the hydrodynamic condition. Grouting is performed under the condition that head pressure, water injection flow, grouting pressure and other parameters are set well, a specially made rubber pad is laid in a test model box, grouting pipes and pressure measuring devices are arranged at corresponding small holes, the outer end of the box is connected with a water injection device, a grouting device and a waste liquid collecting device, slurry preparation is performed, and grouting is performed after water injection is conducted on the device. According to the grouting method under the hydrodynamic condition, a one-dimensional grouting simulation test is performed, the pressure distribution situation during grouting in filled gaps under the seepage condition and the change rule of diffusion with slurry are researched, and the grouting efficiency is improved.