A channel test unit of a digital video recorder (DVR) includes a command generation module generating a selection signal to a controller. The controller outputs control signals to a multiplexer to select an output terminal of the multiplexer to switch to a signal channel. A signal generation module obtains a format voice data and converts to an analog voice signal and sends to the multiplexer. The multiplexer sends the analog voice signal to the selected signal channel after the signal channel is selected. A voice detection module defines an identification (ID) number for each of the signal channels in sequence and detects whether the DVR receives an analog voice signal, and determines whether all of the signal channels have been tested. A display module displays an ID number of the selected signal channel on a display device when the DVR does not receive the analog voice signal.