a method for sequencing a target polymer molecule comprises the steps of : treating the target polymer with an agent that degrades sequentially at least one end of the target polymer ; converting at least a portion of the degraded end of different degraded polymers into a readable signal sequence , and labeling each of said degraded polymers with a tag that represents the relative order of degradation ; determining the sequence of the readable signal sequence ; and determining the sequence of the target polymer using the sequence data obtained in step and the identification of each associated tag .