Taking Fraxinus mandshurica, a main tree species in the temperate zone of Northeast China, as test material, two experimental sites were installed at the altitudes 740 m and 1200 m in Changbai Mountains, respectively, and three precipitation regimes including 30% precipitation enhancement (+ W), 30% precipitation deduction (- W), and naturally occurring precipitation (CK) were designed, aimed to investigate the effects of the variations in precipitation and temperature on the photosynthesis in Fraxinus mandshurica seedlings, with their growth, leaf photosynthetic parameters, and leaf soluble protein and photosynthetic pigment contents examined. Temperature variation had significant effects on the growth and photosynthesis of the seedlings. For the seedlings grown at altitude 740 m, their stem basal diameter, plant height, and leaf chlorophyll and soluble protein contents under the three precipitation regimes had significant increase, leaf carotenoid content decreased, leaf net photosynthesis rate, stomatal conductance, transpiration rate, and stomatatal limitation all increased significantly, whereas leaf intercellular CO2 concentration and water use efficiency had significant decrease, as compared with the seedlings grown at altitude 1200 m. Nonstomatal factors limitation was the main reason for the decrease of the seedlings photosynthetic capacity. Precipitation variation had little effects on the growth and photosynthesis of F. mandshurica seedlings.