Abstract: Phosphorus, as one of the essential elements for crops, has direct contribution to water eutrophication. During summer irrigation in 2008, the soil moisture, phosphorus content of farmland soil, irrigation ditch water, drainage streams water, underground water and soil percolate were monitored, which resulted in phosphorus transportation analysis in Hetao agricultural irrigation area, Inner Mongolia. The data were also statistically analyzed by SPSS13.0 in order to find out the principal factors of phosphorus transportation. The results revealed that，only the soil moisture in topsoil were markedly increased after the summer irrigation, and the soil moisture before and after summer irrigation both significantly correlated with soil depth (Correlation coefficients were 0.751 and 0.770). Meanwhile, available phosphorus (also called Olsen-P) concentration in soil significantly correlated with the soil moisture too (Sig. = 0.009). During the summer irrigation, the phosphorus concentration showed significant difference in different soil depth, but factors such as crop type and cropping pattern did not have notable impacts. After summer irrigation, phosphorus in soil transported to groundwater, mainly in the form of soluble phosphorus. The conclusions in this paper can be used to provide scientific reference on appropriate scheduling for efficient fertilization, irrigation, and controlling phosphorus loss.