A phase field model was developed to simulate hydrogen diffusion and hydrogen-induced cracking of lead zirconate ferroelectric ceramics (PZT-5). In this model, the evolution of hydrogen concentration around a crack in PZT was coupled with stress field analysis by solving both time-dependent diffusion equation and time-dependent Ginzburg-Landau strain field equation. Combined with a fracture criterion, we simulated hydrogen diffusion and crack initiation in PZT ceramics caused by hydrogen ingress from the environment. Numerical results showed that, as the concentration of hydrogen increased, the fracture toughness of PZT ceramics decreased significantly by one or two orders of magnitudes. Therefore, the hydrogen diffusion had a significant influence on PZT ceramics in practical application.