An optical wavelength identifying system comprises an optical wavelength detecting device, a memory, a modulator, a comparison module, and an instruction module. The optical wavelength detecting device comprises a polarizer, a detecting element, a measuring device and a data processor. The polarizer is configured to transform an incident light into a polarized light. The detecting element is configured to form a temperature difference or a potential difference, wherein the detecting element comprises a carbon nanotube structure comprising a plurality of carbon nanotubes oriented along the same direction. The measuring device is electrically connected to the detecting element and configured to measure the temperature difference or the potential difference. The data processor is electrically connected to the measuring device and configured to obtain the optical wavelength by calculating and analyzing the temperature difference or the potential difference.