Aiming at the passive ranging to a noncooperate target, a system based on image sequence from single lens and the respective imaging direction is introduced with its performance. This ranging system does not need initial distance guiding. The distance from target to camera can be estimated by solving a special ranging equation, which is made from target′s characteristic linearity, camera′s coordinates in space, and the target′s azimuth and pitching to the camera. Among these data, azimuth and pitching are obtained by an electrooptical altazimuth. Camera′s coordinates come from a GPS, and the target′s characteristic linearity will be from the image matching between adjacent frames in the image sequence. Analysis shows that the ranging error is mainly determined by the precision of the characteristic linearity, other influencing factors have less impact, which include the measurement error of the target′s azimuth or pitch and the error of the camera′ coordinates. Thus a linearity can be obtained by selecting three matched points in each adjacent frames. These three points have strong Scale Invariant Feature Transform characteristic, with the points a triangle and its circumcircle can be settled. The chord across barycenter of the triangle can be taken as the best characteristic linearity. The experimental result indicates that this ranging method can realize the passive ranging to a noncooperate big target.