Theoretical model and computational analysis are exploited to estimate the electron transfer (ET) due to Paracetamol oxidation. Functionalized electrode surface through HO-BiONO3 based nanocomposite have shown to improve the electrochemical sensor performance from previous experiments. The main aim is to build up an hypothetical transistion state (HTS) model to look at the Bismuth cluster effects on electron transfer rate constant. First, the HTS model based on two Bi atoms cluster is studied as a minimum unit to have a two-electron oxidation process as the Paracetamol one. Then, three Bi atoms cluser based model is drawn to examine a situation in which a free site is close to two reacting sites.