The invention belongs to the field of gene sequencing, and discloses an establishment method for a small fragmental DNA (Deoxyribose Nucleic Acid) library based on an Ion ProtonTM sequencing platform, and a relevant solvent composition solution. The establishment method disclosed by the invention comprises the steps of DNA sample extraction, tail end repairing, fragment selection, joint connection, PCR (Polymerase Chain Reaction) amplification, library detection, high-throughput sequencing and the like, wherein a reagent I, a reagent II and a reagent III are respectively adopted in the steps of tail end repairing, joint connection and PCR amplification. The establishment method disclosed by the invention is precise and simple in step, simple to operate, small in reagent variety and low in cost, the loss and waste of the library are reduced, and the working efficiency is improved; in addition, the establishment method can be applied to noninvasive antenatal diagnosis on pregnant woman peripheral blood fetus chromosome aneuploid based on the Ion ProtonTM sequencing platform, the diagnosis result is high in accuracy rate and is safe and economic, and the birth rate of chromosome aneuploid fetuses can be effectively controlled.