Bone repair microspheres have been widely studied due to their convenience during clinical operations. In this study, beta tricalcium phosphate/sodium alginate/poly(D,L-lactic acid) (β-TCP/SA/PDLLA) composite microspheres were successfully prepared using the liquid droplet method. Then, β-TCP/SA/PDLLA composite microspheres were soaked in simulated body fluids (SBF) for 7 days, and tested in an X-ray diffractometer (XRD). The results indicated that sodium alginate (SA) and poly(D,L-lactic acid) (PDLLA) are not limiting factors for the transformation of β-TCP to HA. Since sodium ions and bicarbonate ions were abundant, the final products were not pure HA but (Na, CO3)-substituted HA. When soaked in SBF, the structure of β-TCP/SA/PDLLA composite microspheres remained stable for at least 14 days suggesting that their anti-washout ability was suitable. Furthermore, the absence of calcination during the preparation of β-TCP/SA/PDLLA composite microspheres enabled the easy incorporation of vancomycin into the microspheres in situ at a final embedding ratio of 26.18%. Furthermore, the β-TCP/SA/PDLLA composite microspheres possessed excellent sustained drug release capability, and the release of vancomycin (92.8 wt.%) lasted for almost 168 h. Our results suggest that the β-TCP/SA/PDLLA composite microspheres could be used as a promising graft material particularly for bone repair.