As people spend considerable time on digital media, online platforms have functioned as major channels for public expression. Understanding the formation and diffusion of sentiment or emotion is benefit to create a healthy environment for public discussion. In this paper, based on emotion contagion and opinion dynamics, we established a specially designed model for dynamic emotion diffusion. The method of computational modelling and simulation is applied to simulate the real-world social interactions. Factors including the distribution of initial emotion, credibility threshold, self-assertiveness and emotion decay function that might influence sentiment diffusion are analyzed, a novel concept of emotion fluctuation is introduced to predict agents’ behavior. Simulation results demonstrate that all these factors mentioned above can influence the evolution of emotion, leading to its fragmentation, polarization or consensus.