A digital signal input circuit including an isolating circuit and a voltage determining circuit is presented, where a first port of an input end of the isolating circuit receives a digital signal, an output end of the isolating circuit outputs the digital signal, and when the isolating circuit is open, the isolating circuit is configured to output a first level, or when the isolating circuit is closed, the isolating circuit is configured to output a second level; and the voltage determining circuit is configured to determine, according to a level of the digital signal, whether the isolating circuit is open or closed. According to the digital signal input circuit, the voltage determining circuit determines a level of a digital signal, thereby correctness of digital signal level conversion is increased.