In this paper, a radio-over-fiber distributed antenna system (ROF-DAS) and wireless positioning mechanism are proposed. The modified Medium Access Control (MAC) frame, optical switch array, ROF network based on star topology and Reflective Semiconductor Optical Amplifier (RSOA) are employed to design the system. A Sigma Delta Modulator (SDM) is employed in the system to optimize the performance of signal transmission. Furthermore, based on the structure, wireless positioning could be achieved by Time Division Multiplexing-Time Difference OF Arrival (TDM-TDOA) technology combined with Chan assisted Taylor algorithm. The improvement of signal transmission quality using SDM is performed by Q Factor, and a comparison of positioning accuracy is performed in terms of the antennas amount using the positioning algorithm.