The tensile plastic deformation behavior of ZrCu-based metallic glass composites with various crystalline volume fractions was investigated. A tensile plastic strain of more than 10 % was achieved in a metallic glass composite with a crystalline volume fraction of 32.6 %. It was found that the B2 phase can effectively activate the formation of multiple shear bands, which significantly stabilize the tensile plastic deformation of metallic glass composites. A critical volume fraction for stable tensile plastic deformation was determined. In addition to the volume fraction, the density of the stress concentration sites and the distribution of the B2 phase were also found to be key factors controlling the stable plastic deformation of ZrCu-based BMG composite.