Degradation of surface modified β-tricalcium phosphate (β-TCP) and poly L lactic acid (PLLA) composite scaffolds were investigated in vitro. Bending and compressive strengths were tested by electromechanical universal material testing machine. Molecular weight changes of lactic acid during degradation were measured by gel permeation chromatography (GPC). Phase composition of the surface after soaking was analyzed by Fourier transform infrared ray (FTIR). The surface and cross section of scaffold samples after degradation were observed by Scanning electron microscope (SEM).The results show that degradation speed can be controlled by adjusting the ratio of β-TCP to PLLA in the composite. PLLA can compound more closely with surface modified β-TCP than with non-modified one. The final compressive strength and bending strength of the scaffolds reach 7.11MPa and 2.20MPa respectively, which satisfies the need for bone tissue engineering scaffolds in clinic applications.