It is still of great challenge to develop green and efficient electrochemical sensors for detection of trace heavy metal ions. In this work, an efficient method was demonstrated for fabricating Palladium nanoparticles (Pd NPs) uniformly decorated porous activated carbon (PAC). The Pd NPs were in-situ reduced on PAC (Pd@PAC) via a KOH activation and thermal reduction method. The morphology investigation suggests that the Pd@PAC possess typical interconnected micropores and mesopores architecture with Pd NPs evenly dispersed on the surface of PAC. The Pd@PAC modified glassy carbon electrode (Pd@PAC/GCE) was used for the detection of trace Cd2+, Pb2+ and Cu2+ ions by square wave anodic stripping voltammetry (SWASV). It exhibited excellent sensitive and selective detection of heavy metal ions simultaneously and individually, together with good anti-interference, reproducibility, repeatability and stability under the same experimental conditions. Moreover, the Pd@PAC/GCE was utilized to detect heavy metal ions in real sample species, indicating potential application in real environment detection. Porous structure and Pd NPs make Pd@PAC excellent electrochemical activity, its interconnected micropores and mesopores architecture accelerate the mass diffusion and facilitate the deposition-stripping process of heavy metal ions. Pd NPs provide more active sites and improved conductivity significantly. The present investigation provides a green and feasible method to assemble efficient electrochemical sensors and electrocatalytic devices.