Abstract: Casting in-site concrete buildings during construction is time-dependent and of importance for controlling the safety and recognizing the properties of its bearing loads. An elastic characteristic value which is defined as the ratio of stiffness of slab to the shore is introduced for the time-dependent structures. A model of continuous beam with spring supports is put forward to analyse time-dependent structural systems. Comparing the results of the model with that of other methods and the results measured from concrete building during construction, good agreement is reached. Principles of bearing loads of time-dependent structural system are given. Position of the maximum bearing construction load of floor can be moved up, when the elastic characteristic value of time-dependent structures were smaller, and the time of shore removal can also change the position of the floor maximum bearing construction loads. The elastic characteristic value of time-dependent structures and the time of shore removal, both have effects on the ratios of maximum construction loads borne by floors. Maximum construction loads borne by floors are of wave form with the position of floor. The lower the position of floor, the larger the wave of construction load, diminishing in the end.