Taking account of the surface effect, the formula for the calculation of the formation enthalpy of nano Ti binary alloys was deduced by modified Miedema model. And the formula was used to study the formation enthalpy of Ti-M (M=Si, Fe, Zn, Tc, Cd, Re, Os, Pb, Bi) nano binary alloys. The results show that the formation enthalpy and structure stability are affected by the grain size for Ti binary alloys with the same composition. That is to say, the smaller the particle size, the greater the formation enthalpy and the worse the structure stability. Also, the component segregation for the nano Ti binary alloys is very clear when the grain size is less than 10 nm. The direction and the degree of aggregation are controlled by the aggregation driving energy.