This paper analysed characters of geology and geophysical fields of northwestern of South China Sea. One steps detail and four steps approach of wavelet transform of gravity and magnetic anomalies of the study area were calculated. According to analyzing and calculating, Bouguer gravity anomalies of study area are negative in northwestern and positive in southeastern. The tend towards of gravity anomalies is NE in eastern and southeastern. The tend towards of gravity anomalies is NW in western. The gravity ...