For the nine characteristic factors of tobacco leaf grading standards have different degree of influence on final grading results and lack of objective evaluation method, in this paper, we applied the gray relational analysis method to determine the weight of tobacco leaf factors in every grade, which calculate the gray relational analysis of nine characteristic factors: such as hue, lightness value, chroma, length, leaf structure, waste, oil, maturity and body. The gray relation was normalized to get the weight of the nine factors in tobacco leaf classification. By contrasted with the subjective evaluation of five experts in tobacco field, the calculation results are basically consistent with the experts’ recommendation. It illustrates that the application of Grey relational method to calculate influence ability of flue-cured tobacco grading factors is feasible. This method eliminates the subjectivity of the weight of each factor and can make the results more realistic.