By multiphase field model method，the unidirectional solidification of eutectic alloy CBr4-C2Cl6 is simulated，and the adjustment of lamellar spacing and morphology evolution have been investigated under three schemes of variable pulling speed，i.e., the stepped change，the linear change and the oscillatory change. The simulation results show that，for the growth under these three schemes，both the interface average velocity and the interface average undercooling show hysteresis effect. When the stepped increase or decrease in velocity is imposed，the lamellar spacing adjustment is realized through abrupt branching or progressive merging and annihilation accompanying the lamellar growing，respectively，and there is strong asymmetry in these two processes during lamellar adjustment. In the case of linear increase in velocity，the lamellar spacing changes by progressive branching，while in the case of linear decrease in velocity，the mechanism of adjustment of lamellar spacing is similar to that of growth under stepped decrease of velocity. The processes for linear increase and decrease in velocity show inverse symmetrical characteristic. A quasi-1λ oscillation mode is present when an oscillatory pulling speed is applied.