Densification behavior of mixed copper and tool steel powder under cold compaction- was investigated. By mixing the yield functions proposed by Fleck et al. and by Gurson for pure powder in terms o f volume fractions and contact numbers of Cu powder, new mixed yield functions were employed for densification of powder composites under cold compaction. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data and with calculated results from the model of Kim et al. for densification of mixed powder under cold isostatic pressing and cold die compaction. Finite element calculations by using the yield functions mixed by contact numbers of Cu powder agreed better with experimental data than those by volume fractions of Cu powder.