Abstract: A quick new method for determining light response curves of photosynthesis under field light conditions has been developed. By using only a potable photosynthesis system (LCA4, UK) under full sunlight condition, we could obtain a series of assimilation rate-light (A-light) response curves by varying the angle of incident light rays to the sensing head to get a series of light intensities (0-2 200 µmo·m-2 ·s-1) which were automatically recorded by the machine, with the corresponding assimilation rates of leaf inside the sensing head being measured simultaneously. Eight arid sandy plant species, ( i.e. Salix psammophylla C. Wang et Ch. Y. Yang, Artemisia ordosica Krasch, Hedysarum scoparium Fisch. et Mey., H. laeve Maxim., Caragana intermedia Kuang et H. C. Fu, Sabina vulgaris Ant., Cynanchum komarovii Al-Iljinski, Psaramochloa mongolica Hitche) were tested by this simple method with good results. During each measurement, environmental variables such as air temperature, air humidity and CO2 concentration but not including leaf temperature changed little, and there existed a significant correlation between the measured data and the predicted data.