The target resolution of line scanners is analyzed quantitatively. It is concluded that its resolution greatly exceeds the limit of instantaneous field of view (IFOV). When the scale of the target or its internal radiance distribution is smaller than the IFOV, we can abtain a distorted, i.e., expanded and boundary blurred response. But if the contrast of target radiance distribution is large enough, this distribution can be imaged and distingushed. Particularly, for linear or spot targets, as long as the contrast or radiance increases by a factor of Sl/St, it can certainly meet the condition of any equations constructed for the distinguishable targets, here SL and ST expresses respectively the areua of the IFOV and the target. If we further make use of the difference of spectral characteristics between the target and background, we can improve the target resolution obviously.