Establishing a simple and accurate method for Hg2+ detection is of great importance for the environment and human health. In this work, platinum nanoparticles (Pt NPs) with different capped agents and morphologies were synthesized. It was found that Pt NPs exhibited peroxidase-like activity that can catalyze the chemiluminescence (CL) of the luminol system without H2O2. The most intensive CL signals were obtained by using PVP-capped Pt NPs as catalysis. Based on the fact that Hg2+ could further enhance the CL intensity in the Pt NPs-luminol CL system, a Pt NPs-catalyzed CL method based on a flow injection system is developed for the sensitive analysis of Hg2+. When the concentration of Hg2+ in the system increases, the CL intensity would together increase, thereby achieving sensitive Hg2+ detection. The limit of detection (LOD) was calculated to be 8.6 nM. This developed method provides a simple and rapid approach for the sensitive detection of Hg2+ and shows great promise for applications in other complex systems.