The invention discloses a device for measuring a sea level uneven horizontal atmospheric aerosol extinction coefficient. A beam splitter splits laser into a first beam and a second beam, the first beam is used for directly injecting to the horizontal atmosphere with a to-be-measured extinction coefficient profile, the second beam is reflected to inject to a photodiode, electric signals are converted from optical signals and then transmitted to a Pico digital oscilloscope, a catadioptric astronomical telescope gathers echo signals scattered back by the sea level uneven horizontal atmosphere, a focusing lens focuses atmospheric backscattered echo signals to a filter, a gated photomultiplier tube is used for converting optical signals into electric signals in a segmented mode, the electric signals are amplified and outputted to the Pico digital oscilloscope, a processor is used for data processing and sending control signals to control the gate opening delay time of the gated photomultiplier tube and adjust the amplified factor of a controlled amplifier module. The device can be used for measuring the extinction coefficient profile of the sea lower atmosphere or called as the atmosphere above the sea horizontal direction.