Disclosed is a high-throughput sequencing method for methylated CpG island in trace DNA, comprising the steps of: 1) treating a DNA sample with bisulfite; 2) adding the treated sample obtained in step 1) to a PCR system containing a primer A for linear amplification; 3) adding an exonuclease having single-stranded DNA cleaving activity to the PCR product in step 2) and inactivating the exonuclease after the reaction; 4) adding the product in step 3) to a PCR system containing a primer B for linear amplification; 5) adding the product in step 4) to a PCR system containing the corresponding adapter primer C and adapter primer D for amplification; and 6) purifying the PCR product in step 5) to obtain a DNA library with a specific length and carrying out the sequencing.