Abstract: An ocean bottom seismometer (OBS) was placed on the seafloor by free fall from the sea surface. Due to the impact of current and bottom topography, the actual position of OBS is usually deviated from the designated position. OBS relocation is the key part of OBS data processing, since the inaccurate position will introduce errors to the geometry and to the following processing. The direct water wave contains the information of OBS position, and the OBS position is inverted from the travel time of direct water wave by the least-square method. The accuracy of shot position, the delay of shot time, the distribution of shots, OBS time drift, errors in picking of first break and the sea water velocity all have impacts on the accuracy of OBS relocation. In this paper, we show the impacts of these factors on OBS relocation, and use some actual OBS in the Dongsha sea area as an example. Numerical results show that to invert the OBS position accurately, the shots should be distributed along a non-straight line. When the offset is less than 10 km, the influence of sea water velocity structure can be ignored. The most influential factor comes from the right-hand error consisting the delay of shot time, OBS drift and picking error. And 5 ms error may lead to 40 m digression. The numerical result agrees with the actual OBS data.