Established wavelength calibrating equipment has been used for precise length calibrating service of measurement devices of laser interferometers and laser trackers for many users. In term of beat frequency for laser wavelength calibrating its measurement value can be traced to the source as length wavelength standard. The wavelength calibrating equipment consists of reference laser, detected laser, optical elements of combined beam, photoelectric detector, wide band amplifier, spectrum analyzer, frequency counter and computer data acquisition system. Influence factors of improving the accuracy of detection are analyzed. Time sampling diagrams of results of beat frequency experiment are given. The basis of judging of relationship between wavelength, frequency and characteristic of frequency stability is also analyzed.