Color measurement instruments designed by principle of photoelectric integral, response of photo detector must meet Luther condition, which is realized by matching of correcting filters, and the matching accuracy is relevant to the actual light path in correcting filter. With the impact of measurement condition, the incident light inevitably contains various directions, and the exist of oblique beams reduces matching accuracy by theoretical calculation. The accuracy of matching filter is evaluated using the smallest proportion of total error area, the theoretical basis for correcting filter matching is introduced, the influence of oblique beams to correcting filter′s matching accuracy is proved, and the corrected formula of thickness of correcting filter is proposed when taking oblique beams into account. Take the matching of “Y” correcting filter as an example, the significant of corrected formula to matching accuracy is proved.