The low-frequency (LF) sky waves can be reflected by the lower ionosphere, so the ionosphere can be detected by analyzing the characteristics of the received signals. The Loran-C is a land-based LF navigation and timing system that can be used for lower-ionosphere remote sensing. The detection strategy in the previous investigations were mainly based on the receiver to get long-distance Loran-C signals, assuming that the received signal was sky waves. As a result, the validity and reliability of the received data are insufficient. In this letter, an LF sky and ground wave monitoring system is developed, which uses high-precision synchronized data acquisition technology and sky-ground wave separation technology to separate and extract sky and ground waves from the received mixed signals, and then to study their characteristics. The accuracy of the proposed system is proved by comparison with the measurement system composed of commercial receiver. The results of the system can be used for remote sensing and detection of the ionospheric $D$ -layer, as well as for studying the effect of space weather on the ionosphere.