A graded pressure drop type multi stage water injection device and method based on fracture observation. The device includes a test probe, a propulsion system and a control system. The test probe includes a plugging device, a pressure conversion assembly and a connected pipe. The rubber bag is wrapped around the outer end of the water leakage pipe, is fixed to both ends of the joints through a fastening iron ring and forms a blocked cavity with the water leakage pipe. The device integrates the plugging and detection system, and uses the same external water source to operate the plugging process and detection process under their respective pressures, thereby making pressure conversion more stable, solving the problem of winding the drill pipe and the hose in the propulsion process, realizing multi stage measurement in each propulsion and improving measurement efficiency.