Clutch system of underground oil casing cutting tool

The invention provides a downhole oil casing cutting tool clutch system. The downhole oil casing cutting tool clutch system comprises a clutch main shaft and clutch teeth which are coaxially connected in a butt joint mode and can be separated. The clutch teeth are telescopically mounted on the clutch countershaft, the clutch countershaft drives the fixed shaft to rotate and extend out along the axis of the clutch countershaft, and the fixed shaft is coaxially and rotatably provided with a cutting blade; the clutch main shaft and the clutch teeth are in one-way ratchet meshing. Retracting and releasing separation and reunion of the blade can be achieved through the ratchet structure, the ratchet structure is integrally combined with the blade retracting and releasing structure, and the structure is compact; by adjusting the direction of the ratchets, the blades can be withdrawn in time and power transmission is cut off when the cutting pressure of the blades is too large; and by arranging the spring, the cutti