Abstract: This paper proposes a simlified method for computing the intenal forces of composite steel girder using the entire cross-section. It involves the solution by the well-known carry-over stiffness matrix technique in which any available computer program may be adopted. Using this method, the response due to concrete creep is obtained by relaxation coefficient approach, which was introduced by prof. Trost. Nevertheless, it can also be extended to effective elastic modulus approach. An example on composite steel girder is given, but it may be used on preflex-girder, composite steel girder in cable-stayed system as well as in concrete composite girder.