Abstract: This paper is a review about the roles of plant osmoticum and its effect on activated oxygen metabolism under stress. The role of proline in removing activated oxygen and the effects of Ca2+ and glycinebetaine on protective enzymes activity and antioxidant content are described.In recent years, molecular biological technology has been widely used in the synthesis of proline and glycinebetain e, which is an effective way for increasing the antioxydization ability of crops and breeding new stress_tolerant varieties.