In this study, numerical investigations are performed on a partially premixed flame of methane and air in two-and three-dimensional models. Nonlinear method is adopted to illustrate the asymmetric phenomenon that affects the flame stability under various co-flow velocities. According to the results, the mathematical relationship between the flame flickering frequency Stanton number and the dimensionless velocity Froude number has been summarized as St=0.7Fr -0.46 . The bifurcation phenomena under different Reynold numbers are found to have significant influence on the system stability. Two critical bifurcation points, which is when Re=300 and Re=1200, are determined as the onset of breaking the flame symmetry and the onset of chaotic state, respectively. The research on flame flicker characteristics provides valuable reference for engineering applications in stable combustion and other related fields.