Bulk metallic glass has aroused intensive interest due to its unique atomic structure and properties, while its structural application is restricted by the shortcomings of its mechanical properties-room temperature brittleness and strain softening. To make up for these shortcomings, various approaches have been proposed, including tailoring intrinsic parameters such as elastic modulus and structural heterogeneity, and changing stress state or defect concentration. Bulk metallic glass composites with ex-situ added or in-situ formed crystallites have been fabricated, series of bulk metallic glasses and their composites with good mechanical properties have been designed, especially TRIP (Transformation-induced plasticity)-reinforced bulk metallic glass composites with large tensile ductility and work-hardening. In this paper, we review the ductilization of bulk metallic glass and its composites, as well as the related mechanism. Particularly, fabrication, properties, structure control and the ductilization mechanism of TRIP-reinforced bulk metallic glass composite are introduced in detail. A perspective of the challenges of ductilization of bulk metallic glassy materials is also mentioned briefly.