Elastic metasurfaces are mostly conceived and designed based on gradient phase and thus suffering from parasitic scattering. Inspired by the advances of surface impedance model in acoustics, in this research, we establish an interface impedance model to realize scattering-free modulation of elastic shear-horizontal (SH) waves. Anomalous refraction at large angle is successfully obtained through interface impedance. Meanwhile, focusing and Airy beam generation are also investigated, which are mostly achieved by phase-based structures. We provide lossless or lossy forms of impedance to suppress parasitic waves. The establishment of boundaries with different shapes has been discussed. Finally, the simulated results of elastic metasurfaces composed of optimized units further validates the feasibility of impedance theory in achieving precise manipulation of SH waves.