With the development of information technology, mainframes still play a pivotal role in civil aviation information systems. The host database is a file-based database composed of multiple database files. It often occurs that the space of a certain database file is abundant, while the space of individual Freespace Record is insufficient, which has an adverse impact on business. FSMonitor is a system used to monitor the Freespace Record space of host database files. It introduces W8236 encoding, RLE compression, and Checksum verification to transfer the FS$SYS file, which records the usage of database files, from the host system to the open system. The file is parsed in the open system for database file usage prediction and intelligent alarm, so as to ensure sufficient database space and the stable operation of the system. At the same time, it reduces the high-cost resource consumption of mainframes.