Abstract: Parasitic relationship exists between bacteria and phages, on one hand, bacteria resist the infection from phages, on another hand, phages develop the abilities against host bacteria. This paper summarizes several kinds of molecular mechanisms related to passive adaptation and active defense on bacteria resistance to phage infection, including physical barrier, adsorption inhibition, preventing phage DNA injection, restriction-modification system and abortive infection, as well as adaptive immune system-CRISPR-Cas system and bacteriophage exclusion system newly found in many bacteria. The competition between bacteria and phages is not only the result of their own selection pressure, but also the dynamics of their co-evolution.