A cutting device with of small-range diameter-variable function of a soft rock shield machine comprises a cutter head, a cutter mounted on the cutter head, a side scraper telescoping mechanism, a hydraulic control device and a wearing limit detecting device, wherein two sides of end parts of at least one slag outlet groove of the cutter head are provided with a scraper respectively; the two side scrapers are left-and-right symmetrical according to the radial centerline of the slag outlet groove and are connected with a telescoping mechanism; the telescoping mechanism is mounted in the slag outlet groove of the cutter head and is driven by a driving cylinder in the hydraulic control device; a displacement sensor is arranged in the driving cylinder; and a wearing limit detecting head of thewearing limit detecting device is arranged on a sleeve protruding along the radius of the cutter head. Compared with the existing cutting device, the cutting device can adjust cutting diameter in a certain range, therefore, the cutting device can improve working efficiency, confirm cutting quality and confirm operator safety.