Objective To monitor healthcare-associated infection (HAI) through a systematic intelligent information-based surveillance system, and gradually reduce the underreporting rate of HAI in the newly built tertiary hospital through continuous improvement measures. Methods Underreporting rate of HAI in a tertiary hospital at the baseline period of the initial establishment stage (from March to December 2021) was analyzed. Under the monitor of a systematic intelligent information system, intervention measures in the first period (from January to October 2022) focusing on informing the usage path of the system and urging timely reporting; in the second period (from November 2022 to June 2023), intervention measures focusing on improving warning strategies and increasing on-site monitoring frequency were implemented. Differences in HAI underreporting rate before and after taking intervention measures were compared. Results The underreporting rate of HAI during the baseline period was as high as 29.14%, which decreased to 5.48% at the first intervention period, and 1.84% at the second intervention period. The diffe-rence in underreporting rates of HAI among three periods was statistically significant (χ²=125.659, P＜0.001). The achievement rate and progress rate of continuous improvement at the first, second period were 123.62% and 81.19%, 142.63% and 93.69%, respectively. Conclusion Based on a systematic intelligent information system, HAI underreporting rate at the early stage of the construction of a newly built tertiary hospital can be effectively reduced by adopting a series of continuous improvement measures.