Due to the restriction of site and cost, no prefabricated beam yard has been built in this project, but cast-in-place. The construction of cast-in-place box girder requires on-site construction and waiting for the solidification of concrete, which takes a relatively long time and cannot be carried out quickly. The construction site conditions of cast-in-place box girder and the ability of construction personnel are different, which are prone to quality problems and cause potential safety risks. Therefore, when pouring small box girder concrete on the support, preparations should be made, including the control of raw material, concrete mix ratio design, formwork reinforcement, and technical disclosure before construction; secondly, the control of the pouring process, pouring method, pouring sequence, and concrete maintenance and mold removal, so as to ensure the quality of box girder concrete after pouring meets the requirements.