Abstract: In order to detect the oceanic red tides based on lidar,the infrared laser can be used to reflect the alga particles'density effectively.The interaction between 1.064μm laser and several marine matters,including water,phytoplankton,yellow substance and suspended particulates was analyzed.The detecting model of 1.064μm laser in the seawater was built.Based on the model and simulation,a conclusion is drawn that the infrared lidar can detect the underwater area within 0.8m effectively so that 1.064μm laser can satisfy the need of detecting the oceanic alga particles'density.