A Yb_(0.11)Gd_(0.89)Ca_4O(BO_3)_3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb_(0.11)Gd_(0.89)COB were calculated to be a=0.8089(7) nm, b=1.5987(6) nm, c=0.3545(8) nm, β=101.22o. The absorption and fluorescence spectra were measured. The maximum absorption cross-section of Yb_(0.11)Gd_(0.89) COB crystal was 0.79×10~(–20)cm~2, which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10~(–20) cm~2. The radiative lifetime trad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb~(3+)in the Yb_(0.11)Gd_(0.89)COB crystal field at room temperature was determined. The ground-state energy level ~2F_(7/2) splitting was calculated to be as large as 1004 cm~(–1) and the zero-line energy was 10246 cm~(–1). A maximum output power of 9.35 W was achieved in continuous-wave(CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb_(0.11)Gd_(0.89) COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed. The Yb_ (0.11) Gd_ (0.89) Ca_4O (BO_3) _3 crystal with new composition was grown by the Czochralski method. The unit-cell parameters of the Yb_ (0.11) Gd_ (0.89) COB were calculated to be a = 0.8089 (7) nm, b = 1.5987 (6) nm, c = 0.3545 (8) nm, β = 101.22o. The maximum absorption cross-section of Yb - ) Gd 0.89 COB crystal was 0.79 × 10 ~ (-20) cm ~ 2, which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33 × 10 ~ (-20) cm ~ 2. The Radiative lifetime trad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb ~ (3+) in the Yb_ (0.11) Gd_ (0.89) COB crystal field at room temperature was determined. The ground-state energy level ~ 2F_ (7/2) splitting was calculated to be as large as 1004 cm -1 and the zero-line energy was 10246 cm -1. A maximum output power of 9.35 W was achieved in continuous -wave (CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb_ (0.11) Gd_ (0.89) COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed.