Doping is an important means to control the properties of diamond. In this paper, the P-doped diamond large single crystals were synthesized by temperature gradient method at 5.6 GPa and 1 312 ℃ using Fe3P as the phosphorus source. The results of the optical micrographs of diamond samples show that as the amount of Fe3P additve increases, the color of diamond crystals becomes darker, the number of inclusions increases in the crystals, and the crystal shape transforms from plate to tower, even to skeletal. It indicates that the V-shaped growth region shifts to the right when Fe3P is added. This is due to Fe3P has effect on the properties of the catalyst. IR spectra of P-doped diamond reveal that the concentrations of nitrogen impurity in the diamond crystals increases with the increase of the Fe3P content. It indicates that the entry of phosphorus induces nitrogen atoms to enter the diamond lattice more easily. Raman spectra results show that with the increase of Fe3P content, the Raman peak positions of the synthesized diamond change little, but the FWHM becomes larger. This suggests that the entry of phosphorus increases the crystal lattice distortion of diamond. XPS test results show that with the increase of Fe3P, the content of P relative to C in diamond crystal also increases. It means that phosphorus are present in the diamond crystals synthesized by Fe3P addition.