In this work, a dynamic S-box is designed based on the chaotic neural network using the memristor model of LiNbO3 (LNO) single crystalline thin film. The LNO memristor, which shows good repeatability and the characteristic of gradual resistance change, is used as the self-feedback weight in the Transient Chaotic Neural Network (TCNN) model to form a chaotic neural network. Double pseudo-random digits are generated for dynamically adjusting the S-box elements according to the weight function. The experimental results show that the proposed design can achieve physical unclonability and has better nonlinearity and differential uniformity.