Taking the 26- and 51-year-old artificial vegetation areas and the natural vegetation area in Shapotou region of southeast Tengger Desert as study sites, this paper measured the net photosynthetic rate (Pn) of algal crusts, and analyzed its relationships with crust water content (> 100%, 40%-60%, and <20%), atmospheric CO2 concentration (360 and 700 mg x L(-1)), and air temperature (13 degrees C, 24 degrees C, and 28 degrees C). The Pn of the crusts in the 26- and 51-year-old artificial vegetation areas and natural vegetation area was 3.4, 4.4, and 3.2 micromol x m(-2) x s(-1), respectively, and the Pn in 51-year-old artificial vegetation area was significantly higher than that in the other two areas. Crust water content had significant effects on the Pn, which was significantly higher at medium water content (40%-60%) than at low (<20%) and high (>100%) water content. When the CO2 concentration doubled (700 mg x L(-1)), the Pn increased by 1.8-3.3 times at medium and high crust water content but had less change at low crust water content, compared with that under ambient CO2 concentration (360 mg x L(-1)). At medium and high crust water content, the Pn at 24 degrees C and 28 degrees C was 27%-66% higher than that at 13 degrees C (P < 0.05), but at low crust water content, no significant difference was observed at the three temperatures.