In this paper, a functional nanoprobe based on graphene oxide (GO) composites was successfully prepared for detection of mercury ion (Hg(II)) with high sensitivity. GO as a substrate was modified and used for the growth of polymer chains to synthesize polyacrylonitrile-grafted GO (PAN-g-GO) by activator generated by electron transfer atom transfer radical polymerization (AGET ATRP). Under the condition of visible light shines, the PANg-GO was further modified to prepare [poly(acrylonitrile-co-vinyl(diphenyl pyridine))]-grafted GO (P(AN-co-PHPY)-g-GO) nanomaterial by one-step synthesis. Finally, P(AN-co-PHPY)-g-GO as a nanoprobe was dropped to the surface of the glassy carbon electrode and assembled to the electrochemical sensor. Moreover, it can effectively improve the enrichment capacity of mercury ions and increase the electron transfer rate on the electrode surface. Differential pulse anodic stripping voltammetry (DPASV) was used to evaluate the electrochemical performance. Under optimum conditions, the response of Hg(II) at this resulting sensor was linear in the range of 2.0 mu M similar to 0.1 nM with a detection limit of 0.06 nM. Additionally, this sensor showed excellent reproducibility, selectivity and stability.