Anisotropy is an intrinsic property of crystalline materials. However, the photoluminescence anisotropy in eutectic crystals of organometallic complexes has remained unexplored. Herein, the eutectic of polynuclear lanthanide complexes and Ag clusters was prepared, and the crystal shows significant photoluminescence anisotropy. The polarization anisotropy of emission δ and degree of excitation polarization P are 2.62 and 0.53, respectively. The rare excitation polarization properties have been proved to be related to the regular arrangement of electric transition dipole moments of luminescent molecules in the crystal. Our design provides a reference for developing new photoluminescence anisotropy materials and expanding their applications. The eutectic of Ag clusters and polynuclear lanthanide complexes induces fluorescence anisotropy. Investigation of the excitation polarization mechanism confirmed that the electrons in the ground state have higher transition efficiency when the direction of the electric field vibration of the photon and the direction of the molecular electric transition dipole moment are parallel.