In this study, the global and local flame responses to the acoustic perturbation were investigated to understand the thermoacoustic features of a low swirl flame. The effects of the Strouhal number and the acoustic perturbation level were examined. The global flame response was investigated with flame chemiluminescence. With the images captured with the planar laser-induced fluorescence of hydroxyl radicals method, the phase-averaged flame surface density was calculated to examine the flame dynamics and the local mean heat release oscillation. The results showed that the Strouhal number was useful in characterizing the flame responses: especially the oscillation amplitude. The flame showed a significant shape deformation when intense flame rollup happened; otherwise, the flame shape deformed weakly. The local analysis showed that large flame deformations caused strong local fundamental oscillations. However, the contribution of the local fundamental oscillation to the global fundamental fluctuation was affected by the local phase distribution, which was associated with the shape deformation characterized by the Strouhal number. The global first harmonic oscillation was generally much weaker than the global fundamental oscillation. The global first harmonic and fundamental oscillations only had comparable amplitudes when the intense local fundamental oscillations tended to cancel each other out.