This paper proposed two approaches to explain the processes of building and developing mental model applied to smartphone applications. Firstly, we developed two versions of money manager smartphone application. And we did empirical studies to collect user behaviors data and built their mental maps to explain how the users build and change their mental model. Secondly, this research tries to describe the underlying mechanism of the development of mental model based on ACT-R cognitive architecture. The proposed simulation model consists of two sub-functions: declarative function and perceptual function.