Because of the different configurations of buildings to be constructed, the arrangement of the whole-raising-scaffold used for practical construction is not always the same, which results in difference of the internal force of the whole- raising-scaffold in application. Based on the abovementioned, in this paper, the design method of the whole-raising-scaffold is investigated, a mechanical model based on the three-span continuous beam is set up, the mechanical characteristics due to the action of various load of the whole-raising-scaffold under the worst working condition is analyzed. Then the calculating method for the internal force of its main structure can be found. Combining the internal force calculated by this method, the security of the scaffold can be verified. The method introduced by this paper can be used as a general method for the scaffold design.