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 .