Abstract: A call cut-off detection circuit for a switch and a method of the same are disclosed. The circuit includes a time switch unit switching a first PCM data, a COB processing circuit combining the first PCM data and a first call state data or separating the first PCM data and a second call state data from a second PCM data, a processor writing the first call state data into the COB processing circuit and judging the state of a call cut-off of a channel based on the second call state data separated by the COB processing circuit, and a local link unit connected between the COB processing circuit and a space switch for transmitting and receiving the second PCM data, for thereby implementing a good quality call and enhancing a reliability of the switch by detecting a call cut-off based on a simple method.