Studies were carried on the mechanism for drought resistance, using stable callus resistant to physiological drought as material. The results showed: The content of dry matter was obviously higher than that of CK. Its water potential was - 10. 76bar, while the water potential of CK was -4. 77bar. Proline content was 4. 4 times as high as that of CK,and the content of k as well as sucrose was slightly lower than that of CK The content of Abscisic Acid was 3. 4 times as high as that of CK.but obviously lower than that of CK stressed on medium containing 20% PEG for four days. New proteins or polypeptides (M. W 17000. 18000 dorton) were produced in the calllus. The property of cell membrane was improved. An assumption of the mechanism for drought resistance was put forward.