The invention discloses a weak rock processing test device and a test method thereof. The weak rock processing test device is used for processing a rock sample and is characterized by comprising a testbed, a lower bearing plate, a connecting rod, an upper bearing plate, a signal control module, a millstone motor, two circumferential constraining devices and an end face polishing module; the connecting rod adopts a telescopic structure; the two circumferential constraining devices are an upper circumferential constraining device and a lower circumferential constraining device; the upper circumferential constraining device is provided with the end face polishing device for polishing the end part of the rock sample; and a cylindrical dull-polishing body is arranged on the millstone motor. Theweak rock processing test device achieves the following beneficial effects: the test device can complete manufacturing of a weak rock standard test sample and provide standard test sample manufacturing guarantee for developing the basic physical and mechanical characteristic tests of the weak rock; and the device is simple in structure, easy to manufacturing, low in cost, convenient to operate, fine in processing, low in injury, high in efficiency and reliable to use.