The invention discloses a method for improving a proportion of fetal
free DNA in a maternal
plasma free DNA sequencing
library. The method comprises the following steps: extracting maternal
plasma free DNA; adding specific sequence tags at two ends of the maternal
plasma free
DNA so as to obtain plasma free
DNA with maternal individual identification markings; subjecting the plasma free
DNA with the maternal individual identification markings to PCR amplification so as to obtain an original
library of maternal individual plasma free DNA; and recovering the maternal original
library in a selected length range so as to obtain a recovered library used for high-
throughput sequencing, or mixing the maternal original libraries of a plurality of different individual pregnant women so as to build the recovered library. The method provided by the invention can accurately detect a sample with excessively low content of maternal
peripheral plasma fetal free DNA, reduces the
sequencing data volume of every sample, improves the sample
throughput of a sequencing reaction, reduces detection cost, and facilitates large-scale popularization.