This study aims to reveal the mechanism of electro-fusion joining of CFRTP composites using multiple Ni-Cr wires as resistance heating element. The materials used for electro-fusion joining test are unidirectional CF/PPS and woven CF/PPS laminates. The effects of electro-fusion condition such as applied voltage and fusion time, Ni-Cr wire spacing and PPS film thickness on the fusion behavior of CFRTP composites were investigated experimentally. The welding area and the joining strength were evaluated quantitatively by microscopic observation and single lap shear test. From the results of surface observation, it was shown that the welding area increased with increasing the applied voltage and fusion time, but thermal degradation and deformation were caused by excess conducting. It was also revealed that Ni-Cr wire spacing and PPS film thickness were significant parameters affecting on welding area and thermal degradation. The optimum electro-fusion condition could be obtained respectively for unidirectional CF/PPS and woven CF/PPS laminates because microscopic electro-fusion behavior was influenced by the fiber reinforcement configuration. Though the interlaminar shear strength (ILSS) is resulted in a marked improvement in the optimum electro-fusion conditions, ILSS was decreased significantly by inserting PPS film which can reduce the thermal degradation. Therefore the experimental results suggested that it is essential to avoid the thermal degradation of matrix polymer by heating of Ni-Cr wire.