A computer program has been developed for the calculation of inter diffusion coefficients from the experimental data of the infinite diffusion couples having continuous diffusion paths in ternary systems. Introducing the least square method for the smooth curve fitting to experimental data over again, one can minimize the shock of inevitable experimental errors to the results of numerical calculation. Using the second integration method of Boltzmann-Matano`s equation, one obtains that the value of numerical calculation is more accurate than that of graphical calculation at extremely lower or upper concentrations especially.