Metal−semiconductor heteronanostructures have attracted increasing attention due to the strong interactions between the two nanoscale-spaced components. Herein, a steerable hydrothermal method is used to control the growth of Ag 2 S shells onto Au nanotriangles with tunable plasmon resonance and local field distribution. Through adjusting pH value and sulfur source, three types of Au/ Ag 2 S heteronanostructures are obtained, including shells on the tips (Au/Ag 2 S (tips)), shells on the sides (Au/Ag 2 S (sides)), and complete shells (Au@Ag 2 S). The surface plasmon resonance and local field confinement are demonstrated to vary with the shell position. Furthermore, compact CdS nanoshells are coated onto the Au@Ag 2 S without any shape change of Au cores. By testing the photodegradation rate of Rhodamine B (RhB) under visible-light irradiation, the Au@ Ag 2 S@CdS hybrids exhibit enhanced photocatalytic activity compared with Au@CdS and CdS. The strong local electric field, the enhanced visible-light absorption, and the optimum band arrangement between Ag 2 S and CdS are thought to be the main factors.