The PDLLA(DL-Poly lactic acids)/HA(Hydroxyapatite) composite and pure PDLLA control were implanted in bone for test. Using fluorescent pictures of tetracycline double label and advanced image analysis system, the trend of bone-formation rate for the implanting region of PDLLA/HA composite was obtained via morphometry measurement of the slices labeled with tetracycline. The investigation and calculation results show that, the formation rate of new bone is stable and high (reaches 2.044μm/day) in the early stage of implantation for the PDLLA/HA composite, demonstrating the advantageous capability of bone formation for the composite. The formation rate of new bone seems to decrease continuously with time, and then the bone formation and bone decomposition tend towards equilibration. Namely, the dynamic balance of bony tissue’s metabolism is maintained.