The paper discusses the capacity of the single observer in a T/R--R type bistatic system without elevation message to locate and track moving targets in three dimensional space. The 3-D location and tracking of moving targets is well achieved by means of the combination of measurement data got at several observation points. Therefore the height message of targets can be extracted from variant measurement values of the difference of distance sum. The feasibility of this way is proved in the paper with the help of simulation.