Goldspur apple (Malus pumila cv. Goldspur) is one of the main fruit trees planted in semiarid loess hilly areas. The photosynthetic efficiency in leaves of eight-year-old trees were studied under different soil water conditions with a Li-6400 portable photosynthesis system and a Li-Cor1600 portable steady state porometer in order to explore the effects of soil water stress on photosynthesis and the suitable soil water content (SWC) for water-saving irrigation of apple orchards. The results showed that the leaf net photosynthetic rate (P (N)), transpiration rate (E), water-use efficiency (WUE), stomatal conductance (g (s)), intercellular CO2 concentration (C (i)), and stomatal limiting value (L (s)) displayed different threshold responses to soil water variation. When SWC was within a range of about 60%-86% of field capacity (FC), P (N) and E were maintained in a relative steady state. At an elevated level but below 60% of FC, both P (N) and E decreased evidently with decreasing soil moisture. The SWC needed to support WUE in a relatively steady state and at a high level was in the range of about 50%-71% of FC. When SWC was less than 48% of FC, g (s) and L (s) declined with decreasing soil moisture, while C (i) increased rapidly. Based on the analysis of the stomatal limitation of photosynthesis using two criteria (C (i) and L (s)) suggested by Farquhar and Sharkey, it was implied that the predominant cause of restricting P (N) had changed from stomatal limitation to nonstomatal one under severe water stress. In terms of water-saving irrigation for enhancing water-use efficiency, it was concluded that in semiarid loess hilly areas, the suitable range of SWC for water-saving irrigation in goldspur apple orchards is in the range of about 50%-71% of FC, and the most severe degree of soil water stress tolerated for photosynthesis is about 48% of FC.