Thank you Meiling XIn and Shabi Abbas Zaidi for answers .
The problem is ,when I using NaOH as electrolyte and after I adding the H2O2 I having O2 gas bubbles surrounding the GCE electrode and if I using N2 gas bubbles to remove the O2 I don't see the oxidation peak .as you see in the image attachment .
That mean the electrode does not detect the H2O2 but its detected the oxygen gas .