Effect of hydrogen fraction on the combustion characteristics of syngas/air mixtures was experimentally investigated at various hydrogen fractions and equivalence ratios in a turbulent combustion bomb under atmospheric temperature and pressure. The laminar burning velocity and turbulent burning velocity at various hydrogen fractions were measured, and the promotion of turbulence on the burning velocity at various hydrogen fractions was systematically investigated. The results show that the laminar burning velocity of the H2/CO/air mixture exhibits a non-linear increasing trend with increasing hydrogen fraction. With increasing equivalence ratio, the laminar burning velocity increases remarkably. Reaction CO + OH = CO2 + H is identified as the most dominate chain branching reactions and reaction H + OH + M = H2O + M is the most dominant chain termination reaction. The laminar burning velocity exhibits linear and non-linear growth with the maximum concentration of radical H and OH, respectively. With increasing the hydrogen fraction, the value of uT/uL shows a non-linear decreasing trend as a whole and the growth rate gradually decreases. As the equivalence ratio increases, the uT/uL value decrease. When the hydrogen fraction is more than 50%, the promoting effect of turbulence on the burning velocity decreases gradually.