Abstract: Aiming at the design and construction characteristics of self compacting concrete for a steel box girder engineering by optimizing the mix design，mixing with the polycarboxylate superplasticizer，fly ash and slag powder for high fluid mixture，adding internal composite expansion source to compensate for the autogenous and drying shrinkage，a C40 non shrinkage self compacting concrete was prepared，and its technical indexes could meet design requirements． Test research shows that self compacting concrete with compound expansion agent dosage being 12%， the slump expansion can be up to 715 mm，segregation rate is only 3. 5%; and there exist residual expansion until 24 h later by the sealing condition curing． By taking reasonable pouring method and temperature control measures， the construction quality was ensured．