This paper proposes a calibration system consisting of three components: a quasi-linear intrinsic calibrator, a linear extrinsic calibrator and a nonlinear L-M optimizer. The focal length is evaluated form vanishing points. Then the rotation matrix and the translation vector are estimated linearly. At last a Levenberg-Marquardt optimization is performed to refine the extrinsic parameters by minimizing the reprojection error. The parameterization of the rotation matrix is discussed in detail, and two parameterization methods, Euler-Angle and Axis-Angle are compared. Experimental results prove that the system can calibrate the cameras precisely.