Abstract: The reinforcement method of externally applied carbon fiber reinforced polymer (CFRP) is often ineffective due to premature debonding of CFRP. This situation can be improved by placing a layer of engineered cementitious composite (ECC) between CFRP and concrete. In order to investigate the factors affecting the bond performance of externally applied CFRP-ECC, twenty specimens were subjected to double shear tests, and the factors considered included whether the ECC surface was polished or not, the tensile strength of ECC, the width and thickness of CFRP, the length of adhesion, and the shear modulus of the adhesive layer, etc. The results show that the ECC surface is not polished, and the ECC is not polished. The results show that ECC surface sanding has a significant effect on the bond relationship, and the ultimate loads of the sanded group of specimens increase by 58.34% to 101.44%. Increasing the thickness of CFRP is a very effective way to improve the bonding performance of ECC-CFRP. Increasing the thickness of CFRP from 0.127 mm to 0.217 mm increases the ultimate load by 54.34%. Increasing the tensile strength of ECC from 0.8 MPa to 2.8 MPa increases the ultimate load by 25.40%. When the tensile strength exceeds 2.8 MPa, the holding length in the ECC becomes shorter due to the higher strength of the ECC, which leads to the reduction of the effective bond length, and ultimately leads to the reduction of the ultimate load. In addition, the shear modulus of the bond layer has a small effect on the bond relationship.