Taking Al-4%Cu hypoeutectic alloy as the research object, the microstructure, changes of solute concentration in solid solution, solute distribution and influencing factors of the directionally solidified single crystal Al-4%Cu alloy with different sample sizes, initial deformation and crystal orientation were studied. The results show that with the increase of the sample diameter, the volume fraction of non-equilibrium eutectic phase in Al-4%Cu alloy increases, the composition curve of Cu solute  becomes more gentle, the distribution of Cu solute in α-Al solid solution solute becomes more uniform, and the ingrain segregation decreases, which is mainly due to the more sufficient natural convection in the melt of the large sample, promoting the diffusion of solute in the liquid phase. The solute enrichment at solid-liquid interface was reduced. After a certain plastic deformation, the dislocation density in the sample increases. The vacancy defects formed during dislocation proliferation and movement can accommodate more solute atoms. As a result, the Cu composition curve increases and solute concentration increases in α-Al solid solution at the initial solidification stage. For samples with different orientations, as the angle of crystal orientation deviating from [001] direction increases, the microscopic segregation first decreases and then increases, while the solute concentration in the solid solution first increases and then decreases.This is because of the anisotropy of the solute atom at the solid-liquid interface. The difficulty of solute atom entering the solid-liquid interface is related to the crystal orientation, and the adsorption capacity of atoms on different crystal planes is inconsistent, which leads to the solute enrichment at the front of the solid-liquid interface and the difference of solute concentration in the solid solution.