The site of oilfield PL19-3 in Bohai is studied in this paper.According to the Chinese Code GB50011-2001

the America Code FEMA-NEHRP and Europe Code EC8

we use the shear wave velocity and borehole data to study the site classification for soft soil site in Bohai seabed.The site seismic effect is analyzed and the influence of the soft soil of seabed on the design ground motion parameters are discussed.The results show that （1） the site classification in active Codes only fit to the land site

it can’t represent the real characteristics of the thicker silt layer of seabed;（2）the soft soil of seabed surface layer puts a remarkable effect on the magnitude and spectrum of the ground motion: the acceleration is magnified significantly due to the nonlinear deformation of the soil and the amplification factor is reduced nonlinearly with the increase of ground motion input;（3）the spectrum is broadened and the characteristic period is extended.The study will put forward the correlate study on the seismic technical codes and design criterion of the oceanic engineering in China.Furthermore

the results of the paper can provide the relate basic data for the seismic design criterion in oceanic engineering and a future seismic zoning of Chinese sea area.