Chemical reactions simulation in detecting hydrogen gas (H2) on Pt80Au14Ti6 sensor surface based on work function change (Δɸ) has been conducted. The simulation result is compared with laboratory results of detecting H2 gas. Three chemical reactions contained three coverages, H coverage (θH), O coverage (θO), and H2O coverage (θH2O). The simulation was run using MATLAB. This research can find the reaction parameter values such as the Arrhenius coefficient of H2O forming reaction on Pt (υf3Pt), H2O forming reaction on Au (υf3Au), i.e., H2O dissociation on Au (υf3Au ), O2 desorption on Ti (υd2Ti), H2O forming reaction on Ti (υf3Ti), and H2O dissociation on Ti (υf3Ti), i.e., 7.5×1014 s–1, 9.85×1015 s–1, 3.25×1015 s–1, 7.11×1015 s–1, 3.425×1015 s–1 and 2.725×1015 s–1, respectively. The simulation results also have the same trend as the laboratory results. However, the contact potential difference (CPD) simulation result, i.e., –240 mV, is not the same as the laboratory result, (–297± 9) mV. In addition, this simulation also obtained approximation coverage for atoms/molecules on PT80Au14Ti6 surface, i.e., θH = 0.665154 Mono Layer (ML); θO = 1.5621× 10–6 ML; and θH2O = 5.41676 ×10–5 ML.