The effects of combined application of magnesium modified biochar and phosphorus fertilizer on phosphorus availability and wheat yield in red soil were studied.Four treatments were set up，including control(CK)，single application of phosphorus fertilizer(P)，single application of magnesium modified biochar(MgBC)and phosphorus fertilizer combined with magnesium modified biochar(P+MgBC).The results showed that the application of magnesium modified biochar or phosphorus fertilizer alone increased the content of soil available phosphorus(AP)，and the content of soil AP in the combined application of magnesium modified biochar and phosphorus fertilizer was significantly higher than that in the treatment of magnesium modified biochar or phosphorus fertilizer alone.The content of soil AP in P+MgBC treatment was significantly higher than that in CK，P and MgBC treatments by 90.4%，34.2% and 59.5%，respectively，and the content of soil AP was significantly positively correlated with phosphatase(Pho)activity，microbial biomass phosphorus(MBP)and soil organic carbon(SOC).Compared with CK treatment，the wheat yield of MgBC and P + MgBC treatments increased significantly，among which the yield of P+MgBC treatment increased the most，with an average increase of 27.1%，but the yield of P treatment was not significantly different from CK treatment.The phosphorus content of wheat plants and grains treated with P+MgBC was significantly higher than that of CK and P treatments，but there was no significant difference with MgBC treatment.The phosphorus uptake of wheat plants and grains treated with P+MgBC increased significantly compared with other treatments，with an increase range of 40.6%～114.3% and 18.7%～58.6%，respectively.In conclusion，compared with single application of phosphorus fertilizer or single application of magnesium modified biochar，magnesium modified biochar combined with phosphorus fertilizer can not only improve the phosphorus availability of red soil，but also improve the yield and phosphorus uptake of wheat，which provides a theoretical basis for the efficient utilization of phosphorus fertilizer in acid soil crop system.