The influence of the ambient light on the wavelength measurement was analyzed theoretically and experimentally. An improved method was proposed to eliminate the influence of the ambient light. By removing the photocurrents caused by the ambient light among the noise-included signal light, the two photocurrents from the dual-junction sensor of the signal light was measured and their logarithmical ratio was first obtained. Then the peak wavelength of the signal light was ealcu lated based on the rdationship between the peak wavelengths of the calibrate light and the logarithmical ratios of their corresponding photocurrents. Finally,an experiment was carried out to compare the measurement accuracy of the traditional and improved methods in the environment involving both of the illumination of daylight and fluorescent lamps. The experimental results showed that the improved method eliminated the influence of the ambient light on the wavelength measurement effectively and therefore enhanced obviously the wavdength measurement accuracy in the environment with the existing of ambient light noise.