Fundamental physics of laminar coflow diffusion flames was numerically studied under bulk flow perturbations. First the numerical method was verified by literature analytical models of linearized diffusion flames. Then it was extended to predict nonlinear characteristics of the full diffusion flame, as well as linearized flame dynamics. In full-precision model without axial diffusion, two petals are found within each cycle of the gain proved resulting from the nonlinear term of the model. A steady strip shows with respect to the forced full flame model, remaining similar tendency to those of both the non-axial diffusion and the linearized models at the same Pe, and changing with St. For the axial diffusion, to smooth the flame wrinkling, a formula is proposed and gives much clearer response oscillations throughout the mixing field than that appearing on the flame sheet. At the burner exit rim, the steady-state flame shows a symmetrical nonlinear distribution between decreasing along the inside- and increasing on the outside wall. The transient position of the flame base shows certain pseudo-sinusoidal oscillation relative to the sinusoidal forcing. Mixture fraction at a point away from the burner wall shows similar response with that at flame base. The scalar dissipation rate was subsequently discussed. (C) 2017 Elsevier Ltd. All rights reserved.