They can be applied to agriculture by changing the properties of biochar by phosphoric acid (H₃PO₄) and pyrophosphoric acid (H₄P₂O₇) . It is helpful to revealing the bio-availability of P on its surface for identifying P occurrence form and binding mode of changed biochar for H₃PO₄ and H₄P₂O₇. This paper adopts wheat stalk biochar (WBC) and cotton stalk biochar (CBC) as raw materials. Meanwhile, this paper prepares changed H₃PO₄ (P-WBC and P-CBC) and changed biochar of H₄P₂O₇ (PA-WBC and PA-CBC) by H₃PO₄ and H₄P₂O₇ respectively. This paper adopts Raman spectroscopy (Raman) and scanning electron microscopy (SEM) to characterize the structure and P distribution of the changed biochar. In addition, this paper adopts Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to investigate the P-binding mode of changed biochar surface. Meanwhile, this paper quantitatively analyzes the changes of P form and content in biochar before and after changing by combining the Hedley phosphorus classification method with visible spectro-photometry. The result shows that the I_G/I_D value of biochar increases and the graphitization structure enhances to form the P-containing granular structure after changing the properties of H₃PO₄ and H₄P₂O₇. It has promoted the formation of carboxyl (—COOH), P—O—P and P—H acid functional groups on the surface of biochar for changes of H₃PO₄ and H₄P₂O₇. They are similar to functional groups on the surface of changed biochar of H₃PO₄ and changed biochar of H₄P₂O₇. XPS result shows that it increases by 13.15%~32.44% significantly by compared with WBC and CBC for the relative content of O1s peak in the changed treatment. Meanwhile, it also shows that it increases by 18.54%~27.02% significantly for the relative content of the P(2s) peak (p<0.05). They have divided P(2s) and O(1s) into C—P—O, C—O—P, O=P—O C=O and (or) P=O C—O—C and (or) P—O—C and P—O—P for the deconvolution integral peaks. It can promote the formation of C—O—P, O=P—O C—O—C and/or P—O—C and P—O—P bonds for the changed properties of H₄P₂O₇ by comparing with the changed properties of H₃PO₄. It also significantly increases the total P content in biochar for the changed properties. Meanwhile, it is significantly higher than that in P—WBC and P—CBC for the P content in PA-WBC and PA-CBC. The active P content in the changed treatment significantly increases by 2.36~14.77 g·kg^-1 compared with WBC and CBC. In addition, the stable P content significantly decreases by 0.06~0.17g·kg^-1 (p<0.05). The active P and moderate active P of PA-WBC and PA-CBC significantly increase by 5.27~15.66 and 0.53~0.64 g·kg^-1 respectively. The stable P content decreases by 0.03~0.34 g·kg^-1 (p<0.05). In conclusion, it has changed the binding mode of P on biochar surface and increased the activity of P for the changed properties of H₃PO₄ and H₄P₂O₇. The difference in the content and binding mode of P in different forms between H₃PO₄ and H₄P₂O₇ modified biochar are of great significance for further exploring the bioarailability of P.