Three desert plants with different photosynthetic types, including C₃ plant Salsola junatovii, C₃C₄ plant S. laricifolia and C₄ plant S. arbuscula, were used to investigate the effect of soil drought stress on the ultramicrostructure of mesophyll cells under pot culture condition using transmission electron microscope. The results showed that: (1) Under the normal water state, the organelles of mesophyll cells kept integrity. (2) Under the slight drought stress, the ultramicrostructure of three plants were not damaged. (3) Under the condition of moderate drought stress, for S. junatovii and S. laricifolia, wall boundary of mesophyll cells were not clear and the thylakoids expanded, but the differences between these two plants were that mitochondria of S. junatovii firstly appeared degradation, and its inclusions were partly lost. For S. laricifolia, the outer membrane of mitochondria was deformed and the ridges were reduced. The mitochondria of S. arbuscula remained normal, but the chloroplasts slightly expanded. (4) Under the severe drought stress, the chloroplasts of S. junatovii and S. laricifolia were damaged and mitochondria were degraded. For S. arbuscula, the chloroplasts expanded, the outer membrane of mitochondria was deformed and the ridges were reduced. These results have showed that the damage degree of S. arbuscula in chloroplasts and mitochondria under different degree of drought stress was the lowest; For S. junatovii and S. laricifolia, the damage degree of chloroplasts under drought stress was similar; the mitochondria had better tolerance to drought stress than chloroplasts in S. laricifolia and S. arbuscula.