In this paper, the phase field method is used to study the multi control factors during directional solidification sidebranching growth of Al-Si alloy. The effects of primary dendritic spacing, pulling velocity, temperature gradient and thermal noise on the evolution of sidebranch are studied. As the primary dendritic spacing increases, the number of secondary branches symmetrically growing on both sides of the primary dendrites increases and the secondary branches are more developed; The increase of the pulling velocity and the temperature gradient can increase the instability of the sidebranch and the degree of solute enrichment in the secondary branches gap. Sidebranch remelting and coarsening will occur when the pulling velocity and temperature gradient are large; Without changing the tip morphology and steady-state behavior of the dendrite, appropriate thermal noise can trigger the sidebranching and make the sidebranch on both sides of the dendrite asymmetrically growth.