The invention belongs to the technical field of a rock mass failure range and permeability measurement, and discloses a rock mass permeability in situ test device. The device comprises a test probe, apropulsion mechanism and a control mechanism, the test probe comprises a rubber capsule, a water leakage pipe, a converter and a communication pipe, the two ends of the water leakage pipe are respectively connected to a joint one, a joint two or a joint three, the rubber capsule is wrapped on the outer side of the water leakage pipe between the two joints, and a certain sealing cavity is formed between the rubber capsule and the water leakage pipe. The inside of the converter is provided with a conical conversion body, a water-passing hole and an annular water tank are respectively formed inthe inside and the surface of the conical conversion body, and a water leakage passage is formed with the hole in the converter. The test device can utilize the switch of a sealing high-pressure watersource to an observation low-pressure water source, achieve work of a sealing process and a test process under the same water source and respective pressures, reduce the number of pipes in a boreholeto one, eliminate the problem of entanglement of a drill pipe and a hose, and improve the stability of the work process.