Human activity recognition based on smart phones has been widely used in many fields including the mobile context awareness and inertial positioning. Compared to the activity recognition whose sensor location is fixed, the activity recognition based on smartphones has a new problem because the mobile direction and position are not fixed. In this paper, we study the activity recognition on the Android smartphones to find out a location-free method. Firstly, this paper analyzes the human motion and experimental data, and proposes a method using the similarity of activity to achieve the location independence to further improve the recognition precision. Secondly we describe how to calculate and use the similarity in the process of activity recognition to help our research. Finally, the experiments are introduced, including the collection of experimental data, results of different methods and the direction of further study.