Abstract An exact solution of solute diffusion for the stoichiometric-compound/stoichiometric-compound eutectic is derived for a planar interface. Compared with the previous work, the solution is consistent with the kinetics of triple-junction, i.e. the eutectic composition is necessarily found at the triple-junction. Adopting an averaged conservation law at the interface, a general solution is proposed for any kind of eutectics and phase diagrams. Simulation results in the Ni5Si2–Ni3Si eutectic growth show that the general solution is a good approximation. The current work makes it possible to incorporate the kinetics of triple-junction into the eutectic growth model.