The invention discloses a DNA library construction method for fetus chromosome aneuploid detection. The method comprises the steps of 1, performing physical interrupting on a sample DNA, and obtaininga fragmented DNA solution; 2, performing tail end repairing and magnetic bead purification on the fragmented DNA, and obtaining the purified blunt end DNA; 3, performing joint connection on the bluntend DNA, and obtaining DNA of the joint; 4, performing PCR amplification on the DNA of the joint, and obtaining a library, wherein according to step 3, the blunt end DNA, nuclear-free water, connection buffer solution, dNTP, DNA ligase, P1 joint and label sequences X are sequentially added into the centrifugal tube and mixed to be uniform, and centrifuging and purifying are performed after the reaction; operation is easy, the flow path is scientific, the standard is clear, and the practical operation effect is good.