The luminescent properties and fluorescence lifetime of Yb∶YAG crystals with different concentration of Yb³⁺-doped were studied. Yb³⁺ ions dopant concentration is 5at%,10at%,20at% amd 30at%,respectively. The absorption coefficients of Yb∶YAG crystals become larger with increasing Yb³⁺ions concentration. Their fluorescence spectra was measured by using LD with a wavelength of 940 nm as the pumping source and TRIA X550 fluorescence spectrum measurement device. The result indicates that lOat% Yb∶YAG crystals possessed the highest fluorescence intensity at the main luminescence band,1030 nm. Simultaneously,the clearly visible luminescence was observed in Yb∶YAG crystals at 450 nm～680 nm bands,and the intensity of which increases rapidly with the increase of Yb³⁺ ions dopant concentration.There are concentration quenching phenomenon in Yb∶YAG crystals. This phenomenon was studied,and the decrease of fluorescence lifetime is attributed to up-conversion emission of trace rare-earth ions and cooperative luminescence of the Yb³⁺ ion.