With the recent 3D display technology improvements, people now can perceive 3D effects in 3D display systems without wearing 3D glasses. However, due to 3D contents are not sufficient enough, the 2D to 3D conversion technique becomes more and more important in the near future. For 2D to 3D video conversion, the most common way is to generate the correspondent depth video from the original 2D video first then synthesizing the desired video by utilizing generated depth videos. The main key point for the 2D to 3D conversion is how to generate the corresponding depth video precisely and efficiently. In this paper, we will propose an efficient depth maps interpolation method from existing pairs of key frames and depth maps. The proposed method contains forward/backward block-based motion estimation/compensation, block refinement, object refinement, and frame selection mechanism. Experimental results show that the proposed method can generate the depth maps successfully and effectively, which will be a great help for 3DTV systems.