The basic idea of calibrating a camera system in previous approaches is to determine camera parameters by using a set of known 3D points as calibration reference. In this paper, we present a method of camera calibration in which camera parameters are determined by a set of 3D lines. A set of constraints is derived on camera parameters in terms of perspective line mapping. From these constraints, the same perspective transformation matrix as that for point mapping can be computed linearly. The minimum number of calibration lines is 6. This result generalizes that of Liu, Huang and Faugeras[12] for camera location determination in which at least 8 line correspondences are required for linear computation of camera location. Since line segments in an image can be located easily and more accurately than points, the use of lines as calibration reference tends to ease the computation in image preprocessing and to improve calibration accuracy. Experimental results on the calibration along with stereo reconstruction are reported.