In Pr3+ and Eu3+ co-doped K2GdF5, efficient energy transfer from Pr3+ 4f5d states to Eu3+ via Gd3+ is observed. The integrated emission intensity ratio of Eu3+ D-5(0,1)/D-5(2,3) upon Pr3+ 4f5d state excitation is enhanced in comparison with the ratio upon Gd3+ I-6(J) excitation. The decay times of Eu3+ D-5(2) and D-5(3) states decrease while those of D-5(0,1) states keep the same with the increase of Pr3+ concentration, originating from cross-relaxation energy transfer between Pr3+ and Eu3+. The simulation demonstrates that the probability density phi(R) of Pr3+ distributing both sides of emitting Eu3+ which substitutes the sites with one-dimensional structure is larger upon Pr3+ 4f5d state excitation than that upon the I-6(J) state excitation of Gd3+.