Objective: This study aimed to develop a low cost and high density lactobacillus starter. Methods: The Lactobacillus fermentum BLHN3 isolated from chopped pepper was used as material, on the basis of MRS medium, the high density fermentation medium and culture conditions were optimized. Results: The optimal carbon source, nitrogen source, buffer salt, growth-promoting factor of L. fermentum BLHN3 were as follows: 30.0 g/L Trehalose, 34.0 g/L Soybean peptone, 2.0 g/L Ammonium citrate, 5.0 g/L Sodium acetate, 2.0 g/L Dipotassium hydrogen phosphate, 10% Carrot juice. The viable count of L. fermentum BLHN3 using the optimized medium was 6.05×109 CFU/mL. We determined the optimal fermentation process using this medium as follows: Initial culture pH was 6, and culture temperature was 37 ℃,inoculum was 3%, and loading liquid was 30 mL. Based on these results, a study of semi-continuous high-density culture was carried out, preferably three centrifugation cultures. Conclusion: The optimization of medium and culture conditions can significantly improve the growth activity of L. fermentum BLHN3, which was significantly higher than that of MRS medium.