In order to study the shear behavior of bonding interface between engineering cementitious composites（ECC） material and existing concrete as well as the action mechanism of shear load, three groups of Z shape direct shear specimens with joints and one group of whole cast in place contrast specimens were designed and tested. The effects of different reinforcement ratios and treatment methods of joints on shear strength, load slip curve, steel strain and shear strength of joints were investigated and compared. The results show that the shear bearing capacity of ECC concrete interface is stronger than that of ordinary concrete under shear load, the shear bearing capacity of specimens treated with keyway is higher than that of rough surface. The shear bearing capacity of specimens is determined by the interfacial bonding force and boundary. The higher the reinforcement ratio is, the smaller the proportion of interfacial bonding force is. The calculation method proposed can calculate the shear capacity and reflect the variation of its components with slip.