In the current work, internal friction and mechanical properties of a Fe41Co7Cr15Mo14-xC15B6Y2Six (x = 0.5, 1, 1.5 and 2 at.%) bulk metallic glasses (BMGs) was investigated. Investigations demons-trated that the Si content could play an important effect on the mechanical properties of Fe-based bulk metallic glasses. The influence of Si on mechanical properties may be related to the structural heterogeneity in the metallic glasses. The quasi-point defects theory was used to describe the structural heterogeneity. Quasi-point defect concentration represents the degree of structural heterogeneity of amorphous alloys. The addition of Si reduces the quasi-point defect concentration in the amorphous samples, and the low quasi-point defect concentration increases the modulus, hardness and fracture strength of the samples. The quasi-point defect concentration of the sample with 1 at.% Si content is the lowest. Results shows that the mechanical properties of amorphous alloy can be improved by adding appropriate an amount of Si.