The evolution mechanism of crystal growth at the initial stage of eutectic solidification in binary hypoeutectic Al-Li alloy under vertical upward unidirectional solidification was studied. The research showed that the primary crystal would grow stably in the mode of regular eutectic at optimized technological parameters while the regular crystal growth couldn’t he obtained due to the disturbance of the melt at unsuitable prameters. The fomiation of lamellar eutectic was attributed to the compositional segregation in master alloy. Surface energy in the grain boundary will lead to crystal defect with different grain orientations.