The invention discloses a detection unit, an ultra-wideband optical detector and a detection method. The detection unit comprises an NbS3 crystal plate and two electrodes, and the two electrodes are respectively arranged at the two ends of the NbS3 crystal plate in the length direction and respectively form ohmic contact with the NbS3 crystal plate. The ultra-wideband optical detector comprises the detection unit and a detection circuit used for collecting potential difference data of the detection unit, and the two electrodes are electrically connected with the detection circuit. The detection method mainly comprises the steps of fixing a detector, irradiating the detector and acquiring detection circuit data. The invention relates to a detection unit, an ultra-wideband optical detector and a detection method. The problem of narrow detection bandwidth can be overcome. The detection bandwidth of the ultra-wideband optical detector ranges from an ultraviolet waveband to a terahertz waveband. The ultra-wideband optical detector has ultra-wide detection bandwidth and has the advantages of high speed and sensitivity.