The replaceable cutter belongs to the back-mounted cutter, which can be conveniently replaced with the disc cutter through the cutter box and mounting wedge under the soft soil, soft rock and pebble strata,and its working height is still the same as that of the disc cutter. The rock-breakingprincipleof thecuteris toutilizetheimpactinertiaenergygenerated by therotation of the cutter disk,through the large cross-section head of the first cutter can be replaced for pebbles, gravel before the cutter disk "hammering" crushing. It can avoid the failure of the disc cutter to break the rock due to the soft rock, pebbles, gravel, which can not be fixed on the palmsurface and the substrate is not strong enough to provide the disc cutter with enough rotating torque and support force for the disc cutter to cut the rock when the hob is digging in the soft stratum.