In this paper, red lemons were used as the main material, the clarification effects of pectinase, complex enzyme, chitosan, bentonite and diatomite on the red lemon juice were studied with light transmittance as the index. The best clarifying agent for the fruit juice was selected. According to single-factor experiments and Box-Behnken experimental design, the optimized clarification process of red lemon juice was obtained. The results showed enzyme and chitosan were better in the clarifying process of the juice. In contrast, bentonite and diatomaceous earth had little effects. Considering the economy, convenience and clarification of the quality of red lemon juice, pectinase was selected a clarifying agent for red lemon juice. The optimum conditions of clarified red lemon juice were: 0.22 g/100mL pectinase, at 50.3 ℃ with pH 4.3 for 62 min, the red lemon juice transmittance was as high as 93.8%.