In this study, plastic flow joining using a shot peening process was investigated. Surface treatment is necessary to improve the surface properties. Shot peening is one of the surface treatments. Since the surface of substrate is hit repeatedly with a large number of shots, the substrate undergoes a large plastic deformation near its surface. Therefore, plastic flow characterized by a shear droop occurs at the edge of the substrate due to shot peening. If an implant made of a dissimilar material is set in a hollow space on the surface of the substrate and then shot-peened, it can be joined to the substrate due to the peening droop generated by the large plastic deformation during shot peening. In this method, the availability of the plastic flow, i.e., the peening droop makes the joining of the implant possible. In the experiment, a compressed-air-type shot peening machine was employed. To examine experimentally the influence of working temperature on bondability, equipment with a heating furnace was produced. The influence of processing conditions on the joining of the implant and the substrate was examined. The joint strength increased with the kinetic energy of shots and processing temperature. The improved implant with a step was effective in improving in bondability. The dissimilar material was also successfully joined to a thin sheet by using of the interaction of peening droops. It was found that the present method using the peening droop was effective for joining the dissimilar materials.