Professor Liu mainly engaged in nitrogen pollution control theory and technology research. More than 60 SCI papers have been published in the authoritative journals in the field of environment, such as environ. SCI. Technol., water res., etc. and cited by SCI for more than 2000 times. Six invention patents have been applied for energy-saving and low-carbon biological nitrogen removal, and two of them have been successfully applied in the industry. He won the gold award of the Young Scientist Award of the society for Environmental Sciences, the Gold Award and the special award of the Geneva International Invention Exhibition.