We reported the large-eddy simulations of a series of bluff-body flames varying air-fuel velocity ratio. The air-fuel ratio y is defined by the ratio of external air velocity to central jet velocity, ranging from 0.05 to 0.50. The case of y =0.32 is exactly same the Sydney bluff-body HM1e flame. Firstly, the mathematical model and numerical method were validated in details as the simulation results are all in good agreement with measurements in HM1e flame. Then the interaction between turbulence and thermochemistry is revealed. As y increases, external coflow trends to dominant the flame behavior. The stoichiometric mixture fraction shifts from the area between recirculation zone and central jet to the area between external flow and recirculation zone. Corresponding, the flame changes from jet-like, columnar to hat-like flames. The different level of local extinction and reignition is also observed. Local extinction and reignition occurs in jet-like and columnar flames. As y increases, local extinction becomes easier and reignition becomes harder.