Generally, 3,3',5,5'-tetramethylbenzidine (TMB) cannot react with hydrogen peroxide (H2O2) in neutral pH or in water at room temperature and pressure. Herein, we found that hexavalent chromium (Cr6+) can trigger TMB reacting with H2O2 (TMB-H2O2) in ultrapure water along with a weak signal output. Then, to implement signal amplification effectively, we designed a ternary nanohybrid material containing graphene oxide (GO) nanosheets, gold nanoparticles (Au NPs), and hyperbranched polyethylenimine (PEI) to form rGO/PEI/Au nanohybrids via chemical bonding. After addition of a trace amount of Cr6+, rGO/PEI/Au nanohybrids can effectively catalyze TMB-H2O2 in ultrapure water; thus, a visual chemosensor and electronic spectrum quantitative analysis method for Cr6+ based on chromium-stimulated peroxidase mimetic activity of rGO/PEI/Au nanohybrids were established. The visual chemosensor exhibits excellent selectivity and interference immunity against 34 other interfering substances with a detection limit as low as 2.14 nM. The visual chemosensor for Cr6+ with a low detection limit and high selectivity is expected to have a potential application in environmental analysis, monitoring, and human health maintenance.