The invention relates to an Nd, Er:GSAG laser crystal and its preparation method. The chemical formula of the laser crystal is Nd<3+>, Er<3+>:Gd3Sc2Al3O12, which can be abbreviated as Nd, Er:GSAG. The molecular formula is Nd3xEr3yGd3(1-x-y)Sc2Al5O12, wherein x is greater than or equal to 0.001 and is smaller than or equal to 0.2, and y is greater than or equal to 0.005 and is smaller than or equal to 0.5. The preparation method includes: taking Nd2O3, Er2O3, Gd2O3, Sc2O3 and Al2O3 as raw materials, mixing them according to a required proportion, and conducting briquetting, then acquiring crystal growth initial raw materials by a solid phase technique, and carrying out orientated growth by means of Czochralski technique, temperature gradient technique, heat exchange technique, Bridgman technique or kyropoulos technique, thus obtaining the Nd, Er:GSAG laser crystal. As a sensitizing ion, Nd<3+> can transfer the absorbed energy to Er<3+> ions in the crystal, thus enhancing the pumping efficiency of laser near 2.7-2.9 micrometers of Er:GSAG. The laser in the wave band has important application in biomedical treatment, optical parametric oscillation, optoelectronic countermeasure and other fields.