Gangdong 1 area in the Dagang Oilfield is a mature oilfield with high water cut, so seismic inversion is the basic task for the deep development of the oilfield. The preprocessing of welllogging data by appropriate technique, therefore, is the key to seismic inversion. Environmental correction was carried out for the mass welllogging data in areas of interest. The welllogging data from different test periods and test equipments were normalized by using the VSP velocity trend as the lowfrequency velocity trend for the acoustic log. Based on the results, the authors studied the acoustic log curves rebuilt through natural potential logs and deep investigation resistivity logs. In order to emphasize the lithologic variation, the authors also probed into the pseudoacoustic log rebuilt with deep investigation resistivity logs, thus providing reliable welllogging data for seismic inversion that can predict formation distribution accurately.