Abstract: The relations between the interface models and the interphase model are studied for particle-reinforced composites . The imperfect interface condition which is equivalent to the effect of a thin interphase for a spherical particle is derived in terms of interface displacement and traction jumps, as is the linear spring interface condition which is equivalent to the effect of a thin interphase. According to the equivalent condition between the linear spring interface and the thin interphase with arbitrary elastic properties, the exact expressions of the spring constants are obtained.The numerical results show that by comparison with the exact solutions of the thin interphase model, high accuracy of the solutions in terms of the imperfect interface and linear spring interface is demonstrated at low modulus ratios of the interphase and the matrix. For the linear spring model, the possible normal interpenetration at the interface is discussed. The conditions for ensuring no interpenetration are established.