Using a CIRAS-2 portable photosynthesis system, the photosynthesis, transpiration, and light responses of Aralia elata were studied under different soil moisture values with the aim of understanding the adaptability of this species to different light and soil water conditions. The results showed that the net photosynthetic rate (P_n), transpiration rate (T_r), and water use efficiency (WUE) of A. elata varied in response to different levels of photon flux density (PFD). When PFD was between 800 and 1,800 μmol m^-2 s^-1, P_n changed little in response to the increasing light intensity, whereas T_r decreased gradually and WUE increased significantly. Light saturation point (LSP) and light compensation point (LCP) were approximately 800 and 30 μmol m^-2 s^-1, respectively. The soil water content had little effect on LSP and LCP, but significantly affected photosynthetic quantum efficiency (Φ) and dark respiratory rate (R_d). By defining the P_n and WUE as the indexes of plant productivity and soil water efficiency, respectively, the soil moisture availability and productivity of A. elata were graded and evaluated, and six types of soil water grading were established. Thus, at RWC values between 44.5% and 79.2% in which both P_n and WUE were maintained at a high level, the results can provide theoretical support for highly productive and efficienct water management in A. elata.