This invention provides a method for reducing the effects of process, supply voltage and temperature variations in integrated circuits and its circuit implementation. The disclosed method builds up a detecting-feedback loop with a plurality of target MOS transistors in main circuits, an induction MOS transistor and a current-to-voltage conversion circuit, and performs a body modulation to effectively reduce the parameter fluctuations of the target MOS transistors in a sub-threshold region or a saturated region due to process, supply voltage and temperature variations. A body-modulated circuit achieves the disclosed method with only a few circuit elements, which effectively improves the stability, reliability and product yield of integrated circuits, especially sub-threshold integrated circuits, without significantly increasing the circuit complexity and power consumption.