Abstract: Time of Arrival (TOA) and Time Difference of Arrival (TDOA) techniques can be used in automatic identification system (AIS) providing ship position information. Which technique should be selected is decided by its positioning accuracy. This study presents accuracy analysis of different positioning techniques used in AIS, including TOA, TDOA and TOA without time synchronization. Position accuracy is derived and analyzed based on positioning models from a Line of Position (LOP) point of view. According to these analysis results it is hard to say TOA or TDOA has the higher accuracy which is depends on the distribution of the base stations. The accuracy of TDOA is always higher than TOA without time synchronization. The simulation results verify the above conclusions.