The invention relates to a graded depressurization type borehole crack detection method, and belongs to the technical field of determination of the rock mining damage range. A used system comprises atest probe, a drilling machine, a drilling rod and a control operating console, the test probe comprises a plugging device and a partial pressure assembly, the partial pressure assembly is connected with the tail plugging device via a communicating pipe and comprises primary and secondary converters, the secondary converter sleeves the primary converter and is in threaded connection with the primary converter, the plugging device comprises a water leakage pipe, a series joint and a rubber capsule, the rubber capsule wraps the water leakage pipe, a plugging cavity is formed between the rubber capsule and the water leakage pipe, and the two ends of the plugging cavity are fixed by fastening loops. The water leakage pipe is provided with water leakage holes, outside water enters the pluggingcavity via the water leakage holes, the rubber capsule is expanded, and a water injection cavity is formed with a borehole. An original operating system is simplified, the problem of drilling coilingis solved, plugging and observation processes are realized via the same outside, and are kept in different pressures, and pressure conversion is more sensitive and more stable.