With high efficiency and high detection precision, the airborne lidar has become an important means to monitor marine environment. Based on the research background of monitoring red tide by airborne blue lidar, a new method of achieving the growth information of red tide alga is proposed, by detecting the concentration of chlorophyll. By this concept, based on analysis of the optical properties of several important ocean objects and bio-optical algorithm, a model is proposed based on airborne lidar detecting backward scattering signals. Simulation proves that the method can monitor the concentration of chlorophyll effectively. It provides a method for red tide detection based on the airborne lidar.