Modern mixed-signal design usually contains multiple power signals with different supply voltages driving different sets of mixed-signal circuit blocks. As the process technology advances to nanometer era, IR drop becomes very significant, which may have great impact on circuit performance and reliability. Insufficient power supply to a circuit block will lead to performance degradation or even functional failure. Although such IR-drop problem can be minimized by widening metal wires or applying mesh routing structures of the power network, excessive metal usage of those power nets with different supply voltages will significantly increase both chip area and cost. This paper presents a new IR-aware routing method to simultaneously route multiple power nets in a mixed-signal design with the considerations of routing congestion, routing tree splitting, wire tapering, and metal layer optimization. Experimental results show that the presented method can effectively reduce total metal usage and satisfy IR-drop constraints.