Abstract:To search an effective approach to preventing tomato bacterial wilt, chitosan were sprayed in tomato inoculated with Ralstonia solanacearum,to study effect of chitosan on bacterial wilt disease and resistance mechanism. The results indicated that chitosan spray induced tomato resistance to bacterial wilt and reduced disease index. The relative cure effect of the treatment 3,in which chitosan was sprayed twice and jiduojing once, reached 48.76%.The peak value of activities of four enzymes, i.e., phenylanine ammonia lyase (PAL), polyphenoloxidase(PPO), peroxidase(POD)and superoxide dismutase (SOD),related to resistance in treatment 3 increased respectively by 46.24%, 51.77%, 121.22%, 36.49%. The contents of chlorophyll in leaves of tomato after chitosan spray were significantly higher than those of normal inoculation tomato.