Abstract: Carbon fiber composites with different degrees of thermal damage were fabricated by changing the heating time. The eddy current impedance signal trajectories of carbon fiber composite specimens with different thermal damage degrees and normal specimens were respectively tested by eddy current detection technology. The change trajectories of eddy current impedance at different test frequencies are compared and analyzed. The test results show that the eddy current detection technology can effectively detect the thermal damage of carbon fiber composites, and the trajectory of eddy current impedance signals change regularly with the degree of thermal loss. With the increase of detection frequency, the more stable the eddy current impedance test signal is, the more effective the test is. The study provides a reference for the future use of this technology to detect the thermal damage of carbon fiber composites and determine the range of thermal loss.