Abstract: Marine radar can be applied to detect oil spill targets in a large range, which cannot be affected by night or cloudy, rain, snow and other inclement weather. It has played an important role in the field of oil spill monitoring. Taking marine radar oil spill image monitored in the "7.16" event in Dalian as data source, based on the principle of marine radar oil spill monitoring, convolution algorithm, Otsu algorithm and mean filtering algorithm are used to denoise the radar image. The effective range of oil spill monitoring is determined by mean operation. Threshold value method and area discrimination method are used to determine the oil film position. Compared with the mean of expert interpretation and C-V level set method, the method of this paper is automatic and more efficient.