The present invention relates to the field of gene engineering, provides a DNA sequencing method and system. Said DNA sequencing method includes following steps: A. said DNA is processed into multiple DNA segments, and then constructed into multiple DNA tags; B. amplification of every single DNA tag, and then processed into single stranded DNA; C. Utilize the anchor which can ligate to DNA tags and possesses at least one degenerated base to sequence every single DNA tag and thus produce sequencing signal; D. Obtain sequences of every single DNA segment by sequencing signal. Said DNA sequencing system, includes: unit of short tags construction, unit of amplification, unit of sequencing reaction and unit of signal processing. In this invention, since DNA tags are sequenced by using sequencing anchor with at least one degenerative abase, length of DNA tags that can be directly sequenced is extended. Both short and long DNA tags can be sequenced. Thus application of DNA sequencing is expanded.