The low temperature hydrothermal carbonization reaction of green algae was studied by combining with the low temperature hydrothermal carbonization technology. The hydrothermal carbon was prepared in the temperature range of 180?C - 240?C. The experimental results had been characterized in detail by oxygen bomb calorimeter, synchronous thermal analyzer and infrared spectrum analysis. The effects of reaction time, reaction temperature and salt concentration on hydrothermal carbonization and combustion were analyzed by studying the experimental conditions under the optimal calorific value. Results showed that algal carbonized, diversity and continental wooden biomass combustion process, and algae in the low temperature hydrothermal carbonization reaction of calorific value significantly increase, and comprehensive consideration of low temperature hydrothermal carbonization algae biomass to improve its calorific value is the best solution to time, salt concentration control in 8 - 10 h, around 0.05%, the reaction temperature is slightly greater than 240?C. It provides a reference for the further research in the field of clean biomass and is of great significance for the development of algal biomass combustion function.