This study reports the development of monitoring method and system for underground condition. The method and the system have been developed to test industrial fields by their microwave signals. In this system, microwaves are transmitted from an antenna on the ground surface into the ground. The echo signals returned from underground targets are analyzed by using signal processing methods such as the synthetic aperture processing. The images of underground condition are reproduced. The results of testing using this method and system are attained the horizontal resolution 30 cm for a diameter of 5cm iron pipes buried at a depth of 1.5m.This underground condition monitoring system has been tested in our fields and can be also applied to underground exploration for not only industrial fields but other kinds of fields such as fields for the remains of ancient.