Abstract: In this paper,the skimmed milk powder was used as raw material to prepare the peptides by fermentation of Lactobacillus paracasei. Fermentation kinetic models were established to compare the fermentation process of the ultrasonic treatment group and the non-ultrasound group. Results showed that the growth of the bacteria in both fermentation processes was consistent with Logistic model. The maximum specific growth rate(X_max)in the ultrasonic group was 14.20% higher than that in the non-ultrasonic group. The product formation of the two fermentation processes conformed to the kinetic model proposed by Luedeking and Piret,in which the product constant(β)associated with cell growth in the ultrasonic group model increased by 99.62% compared with the non-ultrasonic group. The substrate consumption of both processes were in accordance with the Luedeking-Piret model. The yield of the substrate cell growth constant(Y_x/s)in the ultrasonic group model was increased by 14.78% compared with the non-ultrasonic group. The research results showed that ultrasonic treatment could accelerate cell growth,promote the fermentation reaction and increase the fermentation efficiency.