Water regulation caused by enzymes, such as carbonic anhydrase (CA), changes the water status, making it difficult to diagnose water deficit using leaf water potential ((L)) or stomatal conductance (g(s)). Therefore, new methods for timely and accurately determining plant water status should be established. In this study, CA activity, (L), leaf tensity (T-d), photosynthetic characteristics and plant growth of Brassica napus L.seedlings under drought and subsequent rewatering were analysed. Results indicated that T-d could reflect the plant water status better than (L) or g(s) and played an important role in the photosynthesis of B. napus. B.napus exhibited good restorability at the 40gL(-1) polyethylene glycol level. The rewatering strategy for B. napus was excellent at 40gL(-1) (-0.15MPa) 20gL(-1) (-0.11MPa). T-d could be used for the rapid determination of water requirement information in B. napus during winter drought period.