The simplified mechanical model was proposed for framesupported multiribbed composite wall beam. And the internal force of joist was calculated with the method of beam on the elastic foundation which takes the horizontal friction resistance into consideration. Moreover, a comparative analysis was employed with FEA program. It was found that it was necessary to consider the interfacial shearing force between wall and joist for the framesupported multiribbed composite wall beam, otherwise, the performance of the composite would not exhibited sufficiently and the calculation error would be large.