Abstract: As offshore oil exploration wells are mainly situated in the higher part of oil reservoir,oil-water contact of most oil layers hasn't been drilled. Without production testing da-ta,FMT/MDT pressure data will be used to predict oil-water contact. Taking examples of some developed oilfield in Bohai,the oil-water contact comparison before drilling and after drilling has been carried out in this paper. The compar-ison finds that the determination of water line,the number of reservoir pressure measurement points,effective pressure measuring points,the maximum distance between the reser-voir thickness and formation fluid density will affect accuracy analysis of using pressure data to predict oil-water contact.