A simple and ultrasensitive detect method for mercury based on the assembly and disassembly of gold nanorods was proposed. When reduced glutathione(GSH) was added into gold nanorods colloidal solution, Au - S bond will formed on the surface of the gold nanorods. Meanwhile hydrogen bonding and electrostatic interaction prompt self-assembly of gold nanorods (End to End). After mixed with mercury ion, self-assembly of gold nanorods will be inhibition and re-dispersion. Based on above phenomenon, super lower concentration of mercury ion canbedetected used surface plasmon resonance (SPR) of gold nanorods. The lowest detection limit of this method is 1nmol/L when measured by UV - Vis spectroscopy, and the range is from 10 μmol/L to 100 μmol/L when observed by the naked eye. This method for mercury detection based on the assembly and disassembly of gold nanorods can be applied to detecting and monitoring of mercury in environmental.