This paper proposes the Content Diffusion Model (CDM) for modeling the content diffusion process in information-centric networking (ICN). CDM is inspired by the epidemic model and it provides a method of theoretical quantitative analysis for the content diffusion process in ICN. Specifically, CDM introduces the key functions to formalize the key factors that inuence the content diffusion process, and thus it can construct the model via a simple but efficient way. Further, we derive CDM by using different combinations of those key factors and put them into several typical ICN scenarios, to analyze the characteristics during the diffusion process such as diffusion speed, diffusion scope, average fetching hops, changing and final state, which can greatly help to analyze the network performance and application design. A series of experiments are conducted to evaluate the efficacy and accuracy of CDM. The results show that CDM can accurately illustrate and model the content diffusion process in ICN.