By using press-volume technique, this paper studied the seasonal changes of water potential at saturated point (Psissat), water potential at turgor loss point (Psistlp), relative osmotic water content at turgor loss point (ROWCtlp), relative water content at turgor loss point (RWCtlp), relative content of apoplastic water (AWC), bound water/ free water (Va/Vo), and the difference between Psissat and (Psistlp(DeltaP) of Reaumuria trigyna growing on heavy solonchack, non-salinized soil, and saline soil. The seasonal changes of Psissat and Psistlp were in order of May > July > September, while those of AWC, Va/Vo, and DeltaP were in opposite sequence, indicating that the water deficit resistance ability of R. trigyna enhanced with season, being consistent with its growth rhythm. Comparing with other xerophytes, R. trigyna had very low Psissat and Psistlp, presenting its strong ability of maintaining high osmotic pressure and low water potential. Based on the water parameters measured in three months, and by using the subordination function of fuzzy mathematics, the water deficit resistance ability of R. trigyna was evaluated, which was the strongest on heavy solonchack, followed by on non-salinized soil, and on saline soil.