This paper proposes a new localization method using monocular camera. A camera is hanging on the ceiling toward the ground. Its optical axis is perpendicular to the ground as possible. Its intrinsic parameters are calibrated in advance offline. Its extrinsic parameters refer to the chessboard reference are calibrated online. Then a method is proposed to estimate the 3D positions and orientations of the specified arrow targets in the reference frame with only one captured image. The experimental results in indoor environment verify the effectiveness of the proposed method.