Efficient interatomic potentials for Pb(Zr,Ti)O₃ (PZT) crystals, which are intensively applied to ferroelectric devices, are required for the atomic-scale study of the mechanical and electronic behavior of the materials with the increasing demand of further improvement of the devices. In this study, we develop parameters of empirical shell-model potential functions, with which large-scale atomic simulations will be feasible, for the equilibrium lattice parameters and atomic displacements of ferroelectric state and the elastic constants of tetragonal PbTiO₃, PbZrO₃ and PbZr_0.5Ti_0.5O₃ based on first principles calculations. The potentials individually optimized for PbTiO₃, PbZrO₃ and PbZr_0.5Ti_0.5O₃, respectively, reproduce both the structures and the elastic constants of each crystal in good accuracy. The potential simultaneously fitted for all the crystals yields the structural parameters successfully, whereas some components of the elastic constants are poorly reproduced.