With 3D vision measuring, camera calibration is necessary for extracting metric information from 2D images. We present a new algorithm for camera calibration that only requires a spatial triangle with known size. In our method, the camera is fixed while the triangle is rotated freely at one of its vertices. By taking a few (at least two) pictures of the rotating object at an identical camera view position and direction, the camera intrinsic matrix can be obtained. It advances other traditional methods in that the extrinsic parameters are separated from the intrinsic ones, which simplifies the problem with more efficiency and accuracy. Experiments also show that our method is robust and results in high resolution.