This article describes a novel strategy for assembling gold nanoparticles (AuNPs) into chainlike structures and modulating their assembly by surface engineering. The chainlike assemblies are induced to form by adding ethylamine (EA) into a suspension of AuNPs, and the volume ratio of ethanol/water greatly affects the assembly speed and length of the chainlike assemblies. By comparing various structural analogs of EA, it is demonstrated that the primary amine of EA is critically important for AuNP assembly. This study also reveals that besides dielectric surrounding and destabilizing agents, surface engineering also significantly influences the optical properties of plasmonic nanostructures. During this assembly, we have found that two kinds of additives could inhibit or mitigate the AuNP assembly, which were barely reported. The effects of AgNO₃ and halogen compounds, especially KI, on the assembly of AuNPs were studied in detail. Possible mechanisms for controlling AuNP assembly through surface engineering are proposed. Taken together, this study provides a new strategy to regulate the assembly of plasmonic nanoparticles and points out the importance of surface engineering in assembly.