This paper focuses on the influence on the mechanical properties of hydroxyapatite / poly-hydroxybutyrate (HA / PHB) composites by different HA contents, and the effect of Silane coupling agent on improving the interface of HA/PHB composite materials. The HA/PHB composites were prepared by ball milling, hot-pressing, the HA content were 0, 5, 10, 15, 20 and 30wt%, respectively. Silane coupling agent was used for HA surface treatment in HA/PHB composites to compare with not having HA surface treatment in HA/PHB composite materials. The impact strength and flexural strength of HA / PHB composites were tested, and the microstructure of the fracture surface was observed by SEM. The results showed that HA could enhance the bending strength of HA/PHB composites. With HA content increased, the bending strength increased first and then decreased, when the HA content was 10wt%, the maximum bending strength reached 32.74MPa, increased about 41% comparing with pure PHB. Silane coupling agent can improve the interface of HA / PHB, then enhance the mechanical strength. When the HA content was 15wt%, the maximum bending strength reached 46.6MPa, Increased about 56% comparing with the same proportion of untreated HA/PHB composite material, and about double comparing with pure PHB.