The invention provides a buoy for blue algae monitoring and blue algae water bloom early warning, which consists of a buoy carrier, an instrument cabin, a monitoring sensor aggregate, a communication antenna and a solar panel, wherein the buoy carrier supports the whole buoy to float on the water surface, the instrument cabin is fixed on the buoy carrier, the monitoring sensor aggregate is suspended right below the buoy carrier, the communication antenna is arranged on the top of the instrument cabin, the solar panel is arranged on the external surface of the instrument cabin, and a power supply, a control module, a signal receiving / transmitting module, a data recorder, a motor and a sensor position adjustor are arranged in the instrument cabin. The invention can be arranged in lakes, reservoirs or water head sites to monitor effective radiation light intensities, temperatures, dissolved oxygen amounts, blue algae amounts and total alga amounts at different positions and depths in the water bodies with the realization of data real-time transmission.