A concept of incoherently synthetic aperture imaging ladar (SAIL) and its architecture and algorithm is proposed on the basis of computerized tomography (CT) and the detailed analysis and mathematics are given. The feature is that the difficulties in the signal collection and data processing are importantly relaxed. The proposed SAIL has three operations of conventional,inverse and CT spotlight modes,includes two sensing techniques of range resolution and Doppler resolution,and provides a variety of dimensional transformations for imaging that not only for 2-D range or Doppler resolution imaging of 2-D targets but also for 3-D range resolution as well as in the depth compressed 2-D range-resolution and 2-D Doppler-resolution imaging of 3-D targets. Due to the simplification in configuration and diversity of operations,it has a great potential for applications in the extensive fields.