A line terminal for determining operational status of a U interface includes a time presetting module, a current detecting module, a cycle selecting module, a timer, and a synchronization determining module. The time presetting module is for presetting a plurality of time cycles. The current detecting module is for detecting a loop current flowing via the U interface. The cycle selecting module is for selecting a time cycle from the plurality of time cycles. The timer is for timing during the time cycle. The synchronization determining module is for determining if a line terminal has been synchronized with a digital service unit. The operational status of U interface is determined to be working normally when the line terminal has been synchronized with the digital service unit. A method for determining the operational status of U interfaces is also provided.