The invention discloses an automatic spectrum measuring method and an automatic spectrum measuring device. The automatic spectrum measuring device comprises an unmanned automatic navigation ship, and a field spectrometer, an automatic spectrum measuring device and a main control system which are fixedly arranged on the unmanned automatic navigation ship, wherein one end of the automatic spectrum measuring device is fixedly arranged on one side of a ship body, the other end of the automatic spectrum measuring device is connected with the field spectrometer and the automatic spectrum measuring device is used for automatically realizing the multi-angle movement of the spectrum probe of the field spectrometer required for water body spectrum measurement; and the main control system is respectively and electrically connected with the unmanned automatic navigation ship, the field spectrometer and the automatic spectrum measuring device and is used for transmitting path information to the controller of the unmanned automatic navigation ship, controlling the movement of the automatic spectrum measuring device and controlling the measurement and the storage of the spectrometer. The automatic spectrum measuring device has the advantages that the coverage area is wider, the monitoring locations can be flexibly set, the energy is saved when the device is compared with a large ship, the initial cost is low, the entire process is fully automated, the spectrum data, the time, the position and the photos are synchronously obtained, the manmade errors are avoided and the measurement efficiency is improved.