Abstract: Explosion prevention and mitigation technologies for hydrogen/methane gas mixtures represent a critical research area for ensuring the safe application of hydrogen energy. This study systematically investigates the inhibition mechanism of potassium bicarbonate (KHCO3)-containing fine water mist on methane/hydrogen premixed deflagration using a combined approach of experiment and numerical simulation. The results indicate that KHCO3-containing fine water mist exhibits a significant inhibitory effect on methane/hydrogen premixed deflagration, with its suppression performance positively correlated to the KHCO3 mass fraction. Taking the condition of X_(H_2 )=10% as an example, 11 wt% KHCO3 addition resulted in reductions of the maximum explosion pressure P_max and the average rate of pressure rise 〖(dp/dt)〗_avg by 34.64% and 44.57%, respectively. The laminar burning velocity was reduced by up to 66.43%. KHCO3 contributes to suppression through both physical and chemical mechanisms. Physically, droplet phase change (evaporation) absorbs heat and the generated steam dilutes the fuel mixture, thereby lowering the flame temperature and reducing reactant concentrations. Chemically, the decomposition of KHCO3 generates potassium compounds, which undergo the KOH → K → KOH recombination cycle to scavenge key radicals (•H, •O, •OH). This process competes with chain-branching reactions and interrupts the combustion chain reactions.Furthermore, the suppression process is governed by a competition between inhibitory and promotional effects. At high hydrogen blending ratios and high mass fractions, the physical evaporation efficiency becomes a bottleneck that constrains the chemical inhibition, leading to a saturation of the overall suppression efficiency. Nevertheless, a significant inhibitory effect is still maintained.