High-quality Gd_ 0.37Y_ 0.63Ca_4O(BO_3)_3(GdYCOB) crystal was grown for the first time under air atmosphere.The conversion efficiency of noncritical phase-matching (NCPM) third-harmonic-generation (THG) of GdYCOB crystal was measured.The effect of color center on the THG conversion efficiency of GdYCOB crystal was analyzed.The approach to grow high-quality GdYCOB crystal without color center defects was put forward.