The amount of information has been growing rapidly in the open and interactive network environment. And the result comes out not only information-rich, even information overload. How to obtain knowledge in such situation turns to be more and more difficult. User interest model is a key module in the studies of personalized service. In the environment of cloud computing, the User model becomes especially important for the reason personalized service equals to knowledge service. The user interest model is surveyed in the paper in aspects of obtaining and expression of users' interest, and its aim is looking forward to serving construction of cloud of information resource.