Underground space has to be monitored for regional coverage deformations. This issue remains a challenge for current deformation monitoring techniques. In this study, a new high-coverage regional monitoring method is presented to address underground space deformation by using the divergent feature of an ultrasonic sensor. The working principle for coverage regional monitoring, which uses the divergence feature of an ultrasonic beam to increase the monitoring area coverage, is proposed. Space and mathematical models for the ultrasonic beam are also established. An ultrasonic spherical sensor device is designed to achieve all-round monitoring of underground deformation. A longitude-latitude color map histogram is proposed, which enables automatic detection and tracking of omni-directional structural deformation. The new method is illustrated via experiments to determine its validity for deformation monitoring.