To achieve higher-precision reconstruction of flame admittance images in an Electrical Capacitance Tomography (ECT) system, this article presents the design of a low-frequency ECT system. The core is to reduce the system’s excitation frequency, thereby achieving a more optimal balance between the real and imaginary components in the acquired signals. Based on this, the article proposes a specific admittance calculation method tailored to the low-frequency ECT system, which establishes a solid basis for subsequent data processing. Furthermore, considering that parasitic capacitance and impedance within the system can cause phase shift issues in the calculated admittance, the study introduces a targeted phase compensation method to eliminate such interference effectively. Finally, the constructed low-frequency ECT system, in combination with the D-bar algorithm, successfully realizes the accurate reconstruction of both flame conductivity and relative permittivity distribution, offering an effective technical approach for the high-precision detection of flame parameters.