Rotary excavating child-mother drill bit, method and rotary excavating device

The rotary excavating child-mother drill bit comprises an outer barrel and an inner barrel which are coaxially arranged, the bottom end of the inner barrel extends to the position below the bottom end of the outer barrel, a plurality of cutting teeth are arranged on the edges of the bottom ends of the inner barrel and the outer barrel, the inner barrel is a conical barrel with the bottom end diameter larger than the top end diameter, and the outer barrel is a cylindrical barrel. The inner side face and the outer side face of the inner cylinder are both provided with threads, the top end of the inner cylinder communicates with the inner space of the outer cylinder through a notch, the inner cylinder is connected with the outer cylinder through a differential transmission mechanism so that the rotating speed of the inner cylinder can be higher than that of the outer cylinder, and when the child-mother drill bit is used, disturbance to a soil body is small, and bucket cleaning is convenient. 本发明涉及一种旋挖子母钻头、方法及旋挖装