To attain a small caliber millimeter-wave earth observing radar, a wide-band miniature MMW system is needed. In this paper, the miniature system design of a frequency-modulated stepping MMW radar is presented. Firstly, this miniature radar's advantage is analyzed for the need of small caliber earth observing missile. Then, the system configuration is provided to obtain the high range resolution and miniaturization. And in the meanwhile, the method to solve new system problems and optimized selection of system parameters is discussed according to the small caliber terminal guidance radar. At last, experiment results are also given to proven the designed system 's performance.