The conventional laser pen and the storage device are both very small, so they are easy to get lost. To solve this problem, the paper proposes a teaching assistant based on cellphone. The teaching assistant communicates with the personal computer through WIFI, which makes fast-data-transmission come true. The cellphone can control the operations of the PPT, audio, video and test editing. The system sets up on the mobile terminals, and has no special demand on hardware. So, it is easy to use, and in line with the development trend.