Based on conventional camera calibration methods, a flexible approach for misaligned catadioptric camera from planar conic was presented. The catadioptric camera composed of a perspective camera and a hyperboloid mirror. The projection model of misaligned catadioptric camera was built and the projection functions were derived. Having known camera parameters, this method only requires the camera to observe a model plane which contains three concentric conics on the back of the revolution mirror. Then the mirror posture and attitude relative to the camera can be calculated linearly. The center of the concentric conics is on the mirror axis. This technique is easy to use and all computations are matrix operations in the linear algebra. The closed-form solution can be obtained without nonlinear optimization. Experiments are conducted on real images to evaluate the correctness and the feasibility of this method.