A wide-range TSX settlement gauge for dam foundation with deep overburden has been researched and manufactured to overcome the limitation of conventional water tube settlement gauge. The structure, measuring range, precision, sensor type and calibrated results of this settlement gauge are introduced. Its application field, practices and application effect are also given. It’s shown that the measurement by this gauge is consistent with the rules of dam deformation, and thereby could  be used to monitor dam foundation settlement in the long-term with continuous, precise and stable results.