The invention discloses a device and method for monitoring dam foundation stress and aims at providing a device and method which are convenient to use and capable of effectively monitoring the dam foundation stress in real time and are used for monitoring the dam foundation stress. The device comprises a plurality of anchor rods, a plurality of anchor rod stress meters, a plurality of protecting pieces and an exhaust pipe. The anchor rod stress meters are sequentially connected through the anchor rods in a welded mode to form a monitoring body. The outer circumferential faces of the anchor rod stress meters are sleeved with the corresponding protecting pieces. The exhaust pipe is arranged in the length direction of the monitoring body and used for arranging and pulling an instrument cable and extends to the other end from one end of the monitoring body. The method comprises the steps that a hole is vertically drilled in a dam foundation, the device for monitoring the dam foundation stress is slowly placed into the hole, a secondary instrument is used for detecting whether the reading values of the anchor rod stress meters are normal or not, and after detection is qualified, cement mortar is poured into the hole of the dam foundation; the reading values of the anchor rod stress meters at different depths are collected through a reading instrument, and then the stresses of the parts, corresponding to the anchor rod stress meters, of the dam foundation is worked out.