DNA damage is the cause of gene mutation and contributes to cell transformation.The cellular response to DNA damage is complex in its components and regulation. First, DNA repair need cell cycle arrest to avoid mutation accmulating in generated cell. Second, there is strong connection between repair and transcription. Third, nucleotide excision repair and mismatch repair are important pathway of mutation avoidance. If any event mentioned above was altered, mutations would accumulate, and the chance of tumor developing would increase. The relationship between DNA repair,transcription and the cell cycle, and the cell transformation were discussed.