The invention discloses a marine target automatic detection method, and relates to a target automatic detection method. The invention provides an automatic marine target detection method based on space-time analysis of halftone image streams in a visible light range of an airborne photoelectric system of an unmanned aerial vehicle without presetting a hard coded reference image for target detection. The detection method comprises the following steps: S1, acquiring a marine target video sequence of an airborne photoelectric system of the unmanned aerial vehicle; s2, constructing a key target model MO of the ocean scene; S3, obtaining a frame target vector of a suspicious target in a first frame image of the video sequence in S1; S4, updating the key target model MO; and S5, obtaining a frame target vector S6 of a suspicious target in a next frame image of the video sequence in the S1, updating the key target model MO: S7, finding a target with a weight of Wmax from the target vectors ofthe model, and determining the target as a detected target, the Wmax is the maximum allowable weight of the target.