Forty female SD rats were randomly divided into control group， osteoporosis model group （model group），ovarian castratiom and estradiol intervention group （estradiol group），ovarian castration and estradiol combined with 1， 25-（OH）₂D₃ group （estradiol combined with 1， 25 （OH）₂D₃ group）；there were 10 rats in each group.The serum of rats were collected after 24 weeks of feeding， and the levels of alkaline phosphatase （ALP）， osteocalcin （OC），osteoprotectin （OPG），amino-end peptide of type Ⅰ procollagen （PINP），tartrate-resistant acid phosphatase （TRACP） and nuclear factor kappa B receptor activator ligand （RANKL） were detected by ELISA method.Bilateral femurs were taken and the changes of bone tissue were observed by HE and TRAP staining. The elastic modulus， stiffness， maximum stress， maximum lord and bone mineral density （BMD） of bone tissue of the rats in each group were detected by biomechanics and BMD. The mRNA and protein expression levels of ALP， OC， OPG and RANKL in bone tissue of the rats in various groups were detected by RT-PCR and Western blotting methods.

Compared with control group，the levels of serum ALP，OC，OPG，PINP，TRACP and RANKL were significantly increased（P<0.01），the periosteum thickness was increased，the number of osteoclasts was increased，and a little of punctate inset-etched defect was found under periosteum，presenting the typical features of osteoporosis； the biomechanical index and BDM of femurs were decreased（P<0.01），the expression levels of ALP，OC，OPG，and RANKL mRNA and proteins in bone tissue were significantly increased（P<0.01）.Compared with model group，the levels of serum ALP，PINP，TRACP，and RANKL of the rats in estradiol combined with 1，25（OH）₂D₃ group were significantly decreased（P<0.01），the ratio of OPG/RANKL was increased（P<0.01），the osteoclasts in periosteum were proliferated actively，and there was no punctate inset-etched defect；the BMD of femurs of the rats and the biomechrical indexes were significantly increased（P<0.01），and the expression levels of ALP，OC and RANKL mRNA and proteins in bone tissue of the rats were decreased（P<0.01）.Compared with estradiol group，the levels of serum OC and OPG of the rats in estradiol combined with 1，25（OH）₂D₃ group and the ratio of OPG/RANK were increased（P<0.01），the levels of TRACP and RNAKL were significantly decreased（P<0.01），the BMD of femurs and the biomechical indexes elastic modulus and maximum stress were significantly increased（P<0.01），the expression levels of OPG mRNA and protein in bone tissue were increased（P<0.01），and the expression levels of RANKL mRNA and protein were significantly decreased（P<0.01）.

Estradiol combined with 1，25（OH）₂D₃ is more effective in promoting the proliferation and differentiation of osteoblasts， and the combination can reduce the adverse reactions caused by excessive hormone replacement while treating PMOP.