Though the Lovibond colorimetric method is effective for determining oil colour, it is a visual comparison method which relies on manual visual reading. As a result, this method is vulnerable to the influence of subjective factors of testers and is of low accuracy. In this paper, the original index of oil colour grading based on Lovibond colour space is changed to the index of oil colour grading based on uniform colour space, and a new method is proposed to determine oil colour by spectrophotometry. The experimental results show that there is a strong correlation between Lovibond red value and the chroma index a*, and a strong correlation between Lovibond yellow value and the chroma index b*. So the method greatly improves the detection efficiency and avoids a series of disadvantages of the visual method.