Carbon fiber was plated with electroless nickel and then mixed with carbonyl iron to generate wave-absorbing composite coating. The wave-absorbing performance and mechanism of the resulting composite coating were investigated and compared with that of the coating made of carbonyl iron powder alone. The results indicated that the maximum absorbing peak of the Ni-coated carbon fiber/carbonyl iron composite coating was located at -8.89 dB at 5.92 GHz. The corresponding reflection rate was -8.89 dB, and the working band corresponding to a reflection less than -5.00 dB was 9.50 dB. At the same time, the coating made of the carbonyl iron powder alone with the same thickness had a maximum absorbance of -10.36 dB at 7.94 GHz. The corresponding reflection rate for this coating was -10.36 dB, and the working band with respect to a reflection less than -5.00 dB was 6.90 GHz. It was therefore supposed that the carbon fiber/carbonyl iron composite coating of a broader absorbing working band could be suitable to absorbing radar wave.