Because of the advantage of all-weather monitoring, the thermal imager for an offshore oil field security system can monitor the pipeline- and cable-buried submarine area effectively whether it is in fog or at night. An offshore oil field security system based on an infrared thermal imager is designed. The components of the system are given. A single infrared thermal imager system and a combined system consisting of an infrared thermal imager and an automatic Identification System (AIS) are designed respectively. The display and control software for the combined system is designed.