A new technology is proposed based on the hydration heat of concrete. Compared with normal concrete, no matter what kind of pile defects, the release of the heat is on the low side generally in the hydration,setting and hardening process. Mud and other pile defects do not even release heat. Meanwhile, the thermal conductivity of pile defects is poor generally. Concrete hydration heat and the resulting temperature gradient of the large-diameter cast-in-situ piles can be measured accurately, and thus the pile integrity is determined. The technical feasibility has been demonstrated by field trials, which is worth of application and extension based on next thoroughgoing research.