The effects of changing precipitation and wind regimes on plant physiology are increasingly drawing attention of eco-physiologists. In the manipulative experiment we studied the physiological mechanisms of annual C4 herbs in the semi-arid sandy land to understand the functional significance of their traits and responses to the changing environment, grass Setaria viridis, characterized by the moderate stem water content and low leaf water content, more effectively absorbed light energy and utilized water resources than two dominant dicot plants, Salsola collina and Bassia dasyphylla. Precipitation increase and wind reduction promoted photosynthesis of the three C4 herbaceous plants, and their photosynthetic rates were higher in the end of July than that in August. Precipitation increase and the 20% reduction in wind velocity could also enhance their stomatal conductance and transpiration rate. The transpiration rate was consistent with the change in stomatal conductance, exhibiting highly positive correlation. The interactive effects of precipitation increase and wind velocity reduction made great changes in photosynthetic rate of the S. collina, lifted the photosynthetic rate and water use efficiency of the S. viridis. Our results suggest that the C4 herbs have shown some degree of stress resistance, and they are able to acclimate better to frangible environment of semi-arid sandy land. Furthermore, the changing environments heighten photosynthesis of the C4 herbs, which is pretty important to strength the arid plant stress resistance, then contributed to the ecosystem community production and dry matter accumulation.