The invention discloses a stable-phase high-intensity composite cable for underwater detection. A composite sheath is prepared by controlling technical steps and raw material formation of a sheath ofthe stable-phase high-intensity composite cable for underwater detection, selecting calcium carbonate with average grain diameter of 600-2500 meshes and white carbon black with average grain diameterof 2000-5000 meshes; applying secondary mixing, primary open milling, primary extrusion and microwave vulcanization; the sheath material of the cable has high intensity and acid-base resistance property, and is very suitable for using as the cable sheath of the device for underwater detection. Meanwhile, the cable comprises an inner conductor, an insulation layer, an outer conductor layer, a waterblocking layer and a sheath; the cable also has good water blocking performance; the phase angle under the bending and other mechanical conditions is within 4 degrees, thus the stability of the signal transmission is effectively guaranteed.