The second phase in multi-phase alloys has connection with many important phenomena such as aging strengthening, dispersion strengthening, secondary hardening, crystal refinement. In this paper, the interface conjunction factors of the interface between MC(M=V, Nb, Ti) and austenite and martensite are calculate out. The relationship between these factors and the characteristics are analyzed. The reason for the second phases being fine and dispersing and their strengthening and toughening effect on the alloy is explained using the relationship. Based on the relationship, the valence electron structure of the interface between the second phase particles and the matrix can be optimized by changing the alloying elements, which make it possible to design the composition of alloys from the valence electron structure of the second phase particles.