Abstract: To investigate the responses mechanism of phosphorus(P) deficiency stress,the plant growth, nutrient content and physiological and biochemical analysis were performed in Acacia melanoxylon. In this study, A. melanoxylon seedlings were cultivated in Hoagland’s media without P for 3 months and the Hoagland’s media was as the control. Results showed that plant height, stem diameter and number of leaves significantly decreased while the total root length significantly increased under P depletion. The superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were increased in leaves and roots, among which the POD and CAT activity in leaf increased by 113.7% and 473.3%, respectively. Meanwhile, chlorophyll content and net photosynthetic rate (A), light-saturated photosynthesis(A_max) and apparent quantum yield (AQY) also decreased under P deficiency. Besides, nitrogen, phosphorus and potassium in root, stem and leaf also significantly decreased. Interestingly, the P contents in root and stem decreased by 82.9% and 86.8%, respectively. However, nutrient use efficiency indifferent organ showed significantly increased. In our study, we found that A. melanoxylon seedlings have not showed typical P deficiency phenotype although its growth was limited under 3 months of P deprivation.