This paper presents a novel digitally-controlled DC offset calibration (DCOC) circuit for the chopper instrumentation amplifiers that offers better robustness, faster calibration speed, and lower average input noise than traditional integrator-based structures. Different from the traditional analog method, the proposed structure adopts digital circuit to cancel most of the offset introduced by the input-electrode, and the residual offset is eliminated by the second-stage capacitive-coupling amplifier. The difference of two reference voltages is used as the loop-output calibration voltage, so that the system has good temperature characteristic and process characteristic. The noise introduced by the digital offset calibration loop is proportional to the magnitude of the input offset, and no noise is introduced when the input offset is 0V. The circuit is designed in 0.18μm standard CMOS process with the supply voltage of 1.2V. The total power consumption is 36μW and the instrumentation amplifier consumes 7μW. The simulation results demonstrate the effectiveness of the amplifier functionality under different offset voltages, which can eliminate the offset up to ±300mV. Under different offset voltages, the input integrated noise range is 0.67~ 1.49μVrms (0.1~150Hz).