Bias voltage setting have two effects on AlGaN detector,at one set it decide the working status of MOS transistors of the internal two-stage amplifier ;at the other set the ripple wave superimposed on DC can be consider as another noise source,which can coupled to the output of detector.This paper start with factors which may influence the output by theoretical derivation,and then simulate the controbution of single pixel internal op-amplifier bias voltage,reference voltage,power Vdd,power GND to readout noise with spice model，at last show some pictures under different bias voltage settings.All the work aim at supply a suitable,feasible design and configure rules for the ROIC design and detector applier.