The spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants 47Ai, 49Ai, where i = // or ⊥, 47Ai and 49Ai denote the values of isotopes 47Ti3+ and 49Ti3+) of the Ti3+ ions at the tetrahedral Si4+ sites in ZrSiO4 crystal are computed from the high-order perturbation formulas based on the cluster approach where the contributions due to both the d orbitals of central dn ion and p orbitals of ligand ion are considered. The calculated results are reasonably coincident with the experimental values. The defect structure of (TiO4)5− impurity cluster which differs from the replaced host (SiO4)4− cluster in ZrSiO4 is evaluated in the calculation. The results are discussed.