The polyurethane/polystyrene(PU/PSt) composite emulsions with core-shell structure were prepared by seeded soap-free emulsion polymerization．the polyurethane aqueous dispersion was used as seed particles．The thermodvnamie equilibrium morphologies of synthesized PU/PSt composite emulsion particles were predicted using a simplified interfacial tension calculation method based on the minimum interracial energy change principle and validated using transmission electron microscopy and contact angle method．The results showed that the minimum interfacial energy change principie can be extended to PU/PSt system and the simplified inteffacial tension calculation is viable．