An in-situ self-aware adaptive power control (APC) system is presented in this paper. This APC system consists of a voltage sensor, a variable threshold comparator, slack detection circuits and control signal generators to control a set of bidirectional shift registers. The values stored in bidirectional shift registers are used to control the status of multi-mode power gating network. This APC system can suppress power consumption aggressively under different operating speeds. A 16-bit multiplier is implemented as a test bench along with the APC system in UMC 90nm CMOS technology. It exhibits more than 20% overall power reduction under the same speed criteria. The power and area overheads are only 3.64% and 7.36% respectively.