An acid-soluble weighting agent was prepared using hydroxyapatite as raw material and sodium hexametaphosphate as modifier. The chemical structure of sample was characterized by FTIR. The acid solubility，Zeta potential，and wettability of the modified weighted agent were evaluated. Finally，the influence on the rheology and the filtrate loss of drilling fluids as well as the reservoir protection effect was analyzed. The results indicated that the solubilization rate of the modified weighting agent under 10% HCl solution was up to 88.27%. Drilling fluids with modified weighting agents had good rheology and filtration loss reduction properties. The permeability recovery value of the core contaminated by the drilling fluid mixed with modified weighting agent was ＞90% after soaking in 10% HCl solution for 2 h，which showed that the mud cake formed by the participation of modified weighting agents could be effectively dissolved and removed under the effect of acidic，thus protecting the reservoir.