Massive renewable energy is connected to the power grid through the grid-following (GFL) converter. The DC-link voltage fluctuates easily when experiencing challenges, such as grid voltage disturbances and load fluctuation. However, many studies ignore the influence of the DC-link voltage dynamics on the GFL converter. In this paper, the dynamic active current caused by the DC-link voltage dynamics is analyzed for the transient stability of the GFL converter. The dynamic active current would introduce an extra negative damping term in the phase-locked loop (PLL). The estimated domain of attraction (DOA) is obtained through energy function and Lyapunov direct method. Finally, simulation results and experimental results verify the effectiveness of the theoretical analysis.