A touch screen system includes an in-cell type optical touch device for displaying images and receiving a light signal, an out-cell type touch device for sensing a finger or a non-optical stylus, a first functional unit connected with the in-cell type optical touch device, a second functional unit connected with the out-cell type touch panel and a third functional unit connected with the first functional unit and the second functional unit. The out-cell type touch device is disposed on the in-cell type optical touch device. The first functional unit converts an analog sensing signal received by the in-cell type optical touch device into a first electrical signal. An object-sensing signal generated from the out-cell type touch panel is processed by the second functional unit to generate a second electrical signal. The third functional unit analyzes the first electrical signal and the second electrical signal and generates valid output signals.