Abstract: The cast-in-situ reinforced concrete structure is easy to crack on the wall and cause leakage when it is too long. The prevention and control of cracks is the key point to be considered during the design. This paper analyzes the reasons for cracks in reinforced concrete water tank from the aspects of load, dry shrinkage, temperature and humidity difference, material quality, joint structure and construction. For the construction of a large fire water tank, expansive concrete was used to prevent dry shrinkage crack during construction, and the temperature stress was calculated through ambient temperature difference during service to ensure that the temperature stress is less than the tensile strength of concrete, so as to avoid structural cracks. The project has been operated smoothly for many years since it was put into use

Key words: fire water tank, crack, control, expansive concrete