The spectra of absorption, excitation and emission of ZnWO4:Er crystal were measured and studied. There is an energy transfer process between Er3+ ion and the host lattice. Intensity parameters Ωλ of Er3+ in ZnWO4:Er crystal were calculated based on Judd-Ofelt theory. The oscillator strength, spontaneous radiative transition rate, radiative lifetime, integrated emission cross section and branching ratio were calculated and discussed. The authors believe that the crystal has the potential usage as a lasing material.