DNA polymerase beta (pol beta), a predominant enzyme involved in DNA base excision repair (BER), plays an important role in repair of DNA damage and maintaining stability and integrality of genome. Pol beta lacks 3' to 5' proofreading activity, which contributes to its low fidelity in DNA synthesis. There are different results about action rule of pol beta in genetic instability and mechanism of pol beta in tumorigenesis. The structure and function of pol beta, the relationship between pol beta and genome instability, and abnormal expression and mutation of pol beta in tumor were reviewed.