Disclosure is to a mobile apparatus having an optical indexer, and a method for performing indexing. The mobile apparatus includes an optical indexing module for sensing a movement. A control interface is generated in simulation and displayed on the mobile apparatus as it apparatus operates as a computer mouse. In the method, the simulated control interface is initiated in the beginning. The optical indexing module is activated to perform a tracing process, in which the optical indexing module emits a light and receives, especially by the multiple sensing cells arranged in an array, the reflected light. The photo energy received by the every sensing cell within a time slot can be computed. The energy difference in the time slot is used to determine a moving direction. An indexing signal is generated by converting movement signal made by optical indexing module and control signal from the simulated control interface.