Abstract: A new simple method is proposed for light wavelength measurement.The ultrasonic diffraction spectra of mercury and He-Ne lasers through ethanol solution（97%） are analyzed.Using the He-Ne laser wavelength as the standard value,the wavelengths of yellow light,green light and blue light in mercury are calculated.The relative errors between the calculated and the standard values are 0.38%,1.0% and 0.60%,respectively

Key words: ultrasonic diffraction grating, mercury, He-Ne laser