Abstract: To solve the problems of insufficient measurement accuracy of filter rod diameter and inability to measure cavity filter rods, the diameter measuring device based on air pressure in KDF2 filter rod maker was replaced by an optical diameter measuring device based on a Charge-Coupled Device (CCD) sensor. By analyzing and modeling the noise of CCD output signal in practical application, a sinusoidal fitting method based on Fourier series residual correction (SFM-FSRC) was proposed to replace the traditional polynomial fitting method in the process of signal binarization, so as to realize the accurate fitting of boundary data and avoid the influences of large vibration and noise on the measurement accuracy of filter rod diameter during the operation of KDF2 filter rod maker. The optical diameter measuring device with traditional polynomial fitting method and SFM-FSRC was compared on a KDF2 filter rod maker with a standard rod of 5.400 mm diameter and produced cavity filter rods of 5.300, 6.300 and 7.600 mm diameter. The results showed that, compared with polynomial fitting, the relative error of the measured standard rod diameter narrowed from a range of -0.65% to 0.39% to that of -0.04% to 0.19%, and the standard deviation of the cavity filter rod diameter reduced from around 0.030 mm to around 0.010 mm. This technology provides technical support for improving the quality and consistency of filter rods.