Based on the zeros of the time-averaged complex scalar field, the complex scalar field of Riemann-Silberstein (RS) vortices generated by the edge dislocation line embedded in the Gaussian beam propagating through the bifocal lens is derived. The focal characteristics of the RS vortices are studied in detail, and the influence of the propagation distance and the focal length of the bifocal lens on the RS vortices is nalyzed. It is found that the RS vortices will move after passing through the bifocal lens, a new pair of RS vortices with opposite topological charge will be generated, and two RS vortices with opposite topological charge will gradually approach each other to annihilation. However, during the entire focusing process, the total topological charge of the RS vortices is conserved. In particular, when the RS vortices pass through an ideal lens, there are always only four RS vortices on the x-axis in the complex scalar field. As the propagation distance increases, these four RS vortices gradually approach the origin (0, 0), and then gradually move away from the origin (0,0), but the topological charge of each RS vortex has remained unchanged, thus the total topological charge is conserved.