Abstract: The paper aims to study the effect of pH stress on photosynthetic physiology of lemon saplings, and determine the optimal soil acidity and alkalinity for expanding lemon growth in Yunnan Province. A pot experiment was conducted and 1 year old lemon grafted saplings were grown in soil with different acidities (adjusted the soil pH value with HCl and CaO) to test the photosynthetic parameters and chlorophyll content of lemon leaves. The results showed that soil pH value had ignificant influence on net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), water use efficiency (WUE), chlorophyll a (Ca), chlorophyll b (Cb), carotenoid and chlorophyll a + b (C T) (P <0.05), with the highest intercellular CO2 concentration (Ci), stomatal conductance (Gs) and transpiration rate (Tr) obtained under soil pH 7-8. Meanwhile, chlorophyll a, chlorophyll b and chlorophyll a+b were also the highest under soil pH 7-8. Therefore, the suitable range of soil pH value was 7 to 8 for‘Yunning 1’cultivation, while overly basic or acidic soil inhibited photosynthesis and growth.