Zr52. 5Cu17. 9Ni14.6Al1.0Ti5 bulky glass sheets with thickness of 2mm were prepared by a water-cooled copper mold casting. The volume fraction of quenched-in crystallines were controlled by changing oxygen impurity content and overheating level. The results show: low oxygen content and enough large overheating level can improve the glass formation ability of the present ahoy. Fully amorphous sheet with a thickness of 2mm displays high fractured strength (1 710MPa). Samples with volume fraction of 2% still have high fractured strength (1 580MPa), but that of samples with volume fraction of 7% reduce rapidly to 1 220MPa. The reason for decreasing of fracture strength is that quenched-in crystals embedded on the amorphous matrix induce initiation and propagation of crack.