In this paper, a novel application of harmonic ranging system will be illustrated. With the combination of the binary phase-shift keying (BPSK) and the spread spectrum technique, the harmonic ranging system is able to determine the range of the target more accurately, especially to tiny targets, such as small insects. The autocorrelation properties of pseudo random noise (PRN) used in the spread spectrum technique provides the possibility to develop a new ranging system for tiny targets over the original harmonic ranging system. And the BPSK modulation is adapted here to merge the PRN into the harmonic ranging system. On the other hand, there are other limitations caused by the size of tiny target. The tiny targets such as small insects are usually not able to carry large size or heavy devices over them. Thus, a light weight and small dimension transponder is required here to provide the ability to reflect the signal back to the base station for ranging the distance of the target. And the gigahertz operation frequency makes the requirement of design become possible.