<p>With the evolution of nickel-based single crystal superalloys, there is an increase in heavy elements such as Re and Ru. This has made solutal convection more pronounced during the directional solidification process, leading to solute redistribution and increasing the risk of casting defects such as low-angle grain boundaries. To avoid casting defects, downward directional solidification (DWS) method is adopted to eliminate solutal convection and change solute redistribution. However, there is currently no in-situ characterization or quantitative simulation studying the solute redistribution during DWS and upward directional solidification (UWS) processes. A multicomponent phase field simulation coupled with lattice Boltzmann method was employed to quantitatively investigate changes in dendrite morphology, solutal convection and deviation of dendrite tips from the perspective of solute redistribution during UWS and DWS processes. The simulation of microstructure agrees well with the experimental results. The mechanism that explains how solutal convection affects side branching behavior is depicted. A novel approach is introduced to characterize dendrite deviation, elucidating the reasons why defects are prone to occur under the influence of natural convection and solute redistribution.</p>