Abstract: The external environment and geological conditions of offshore mass concrete structure are quite complex. For the sluice structures with cracks, because of the geographical position, climate changes and tidal water level fluctuation, the cracks in the sluice pier are in a state of tension, which reduces the stability of the sluice structure and even affects their service life. The actual monitoring analysis of the changes in the coastal environment temperature has a certain value for the safety and durability evaluation of the concrete structures. Therefore, taking the Yongding New River sluice gate works placed on the typical soft soil foundation as a case history, the pier crack width is monitored by the crackmeter. The studies of influences of environmental factors during the period of operation (mainly atmospheric temperature, water temperature and tide level fluctuation) on the cracks of the piers are carried out in this paper. The health and safety monitoring software is adopted to process the measured data. From the analyses it is found that the environmental temperature and water level fluctuation are the sensitive factors affecting the variation of underwater crack width of the pier. The study provides a new idea for the safety maintenance and prevention of the cracks in the floodgate piers in the future.