Abstract: Citrus peel residue, which from local fruit juice production, was used as the raw materials in this study. The carbon-nitrogen ratio was determined through methods of potassium dichromate and Kjeldahl distillation, while the effect of the amount of sulfuric acid on the measurement results was explored. The results showed that: when the weight of raw materials was about 0.3 and 0.1 grams, the optimum amount of sulfuric acid was 50 mL and 6 mL for the methods of potassium dichromate and Kjeldahl distillation, respectively. The carbon-nitrogen ratio of 36 was obtained under the experimental conditions.