A technique of diffusive gradients in thin films (DGT) was developed for the in situ measurement of reactive phosphorus species in natural waters, sediments and potentially soils. Polyacrylamide / basic magnesium carbonate was used as the novel binding phase of DGT. Various factors, such as initial concentration, deployment time, pH and ionic strength, which may affect the adsorption of phosphate to the DGT were investigated. H2 SO4(0. 25 mol/ L, 10 mL) was used for elution of phosphate from the binding gel, and an elution efficiency of 85±5% was obtained. The DGT measurement was independent of ionic strength (0. 001-0. 05 mol/ L) and pH (4. 10-9. 15). The results indicated that the maximum adsorption capacities of DGT were limited to 20. 4 μg per disc ( T = 25℃, pH = 7. 00, [ P] = 2 mg / L). Good agreement was obtained between the measurement results of DGT method and molybdenum blue method in the P concentration from 0. 001 to 20 mg / L. The method detection limit (MDL) was 102. 4 ng / L. Field performances of DGT in synthetic seawater, the coastal seawater of Xiamen, Lake Yihai, Lake Chaohu and Nanfei River indicated that the basic magnesium carbonate-DGT method was more reliable than the commonly used ferrihydrite-DGT method.