Abstract: By the action of long term loads， the steel-concrete composite beams will undergo additional deformation due to concrete shrinkage. The existing Chinese specifications do not consider in detail the impacts given by this additional deflection on long-term deformation of the composite beams. This paper analyzes and studies the computation theory with regards to concrete shrinkage in the domestic and foreign literatures， tables the composite beams′ additional deflection calculation formula reflecting the concrete shrinkage and strain， calculates the actual shrinkage effects of two typical composite beams of an actual engineering project， performs the simulated deformation calculation of the composite beams under the shrinkage effects by the finite difference simulation software FLAC 3D，and compares the various calculation results. Calculation， FLAC 3D numerical simulation as well as the comparative analysis results of the actually measured data show that the shrinkage calculation method based upon Australian Standard (AS3600-1988) of this formula approximates most of the simulated values and measured values， and can be used for long term additional deflection calculation analysis of the composite beams.