To reduce the cost of HA and improve degradation performance of HA, oyster shells were used as raw materials to prepare CaCO₃/ hydroxyapatite (HA) composite materials by a hydrothermal method. Phase analysis and SEM/TEM observation revealed that as-prepared CaCO₃/HA composites had a morphology of HA nanoparticles growing on the lamellar CaCO₃. Three kinds of CaCO₃/HA composites (20%HA、40%HA、60%HA) with HA content of 20%, 40% and 60% were prepared by controlling the proportion of calcium and phosphorus. The actual content of HA in three obtained different composites, determined by ICP, were 17.52%, 34.30% and 43.24%, respectively. With the increase of HA content, the specific surface area and thermal stability of CaCO₃/HA composite are improved. Samples were immersed in PBS simulated body fluid for 14 d to evaluate their in vitro degradation ability. The results showed that degradation rates of three kinds of composites with different HA contents (20%HA, 40%HA and 60%HA) were 15.2%, 12.0% and 10.8%, respectively. The degradation rate decreased with the increase of HA proportion in the composite. All data indicates that the hydrothermal synthesis of CaCO₃/HA composite can control the conversion degree of HA and then adjust the degradation rate of CaCO₃/HA composite by designing the ratio of calcium and phosphorus elements, which have potential application in orthopedics.