Abstract: A colorimetric method was developed for the determination of trace amount of H2O2 in acidic 2-(N-morpholino) ethanesulphonic acid buffer medium, based on surface plasma of gold nanoparticles. The detecting system, whose limit of detecting resolution with naked eyes was measured previously, was used to accurately quantify the concentration(c) of H2O2 by spectral analysis after stabilization enhancement. The results show that blue-coloured solutions with aggregated gold nanoparticles could be obtained when c100 mol/L, while the solutions were red-coloured with non-aggregated gold nanoparticles when c120 mol/L. The resolution limit of human eyes to this detection system was able to distinguish H2O2 concentration difference of 20 mol/L. However, the color distinction of solutions was unstable and has a quick change in 45 mins. The blue solution with c of 60 to 100 mol/L turned red gradually. The OD_570 of solutions also demonstrates that the reaction was constantly changing in 3 h after detection. Moderate L-glutathione was added to terminate the reaction after 10 min to improve the detection stability, which can stabilize the color distinction and effectively keep a constant OD_570. The spectra of the nanoparticle dispersions show the absorption peak at 550 nm and there is a positive correlation between intensity and the H2O2 concentration when c100 mol/L. The absorption peak shifted to 540 nm when c120 mol/L. By the spectral analysis, a linear relativity of regressive curves of OD_630/545 and the concentration of H2O2 was found. Then solutions with c from 100 to 120 mol/L were detected and accurately quantified H2O2 with concentration difference of 2 mol/L to break the limit of detecting resolution. The detection system could provide a preferential platform for trace detection.