Abstract: A new type of prestressed steel box-concrete composite beam is proposed，whose advantages and applicability were analysed，the formula of ultimate capacity and the fiber model method of the structure were researched as well． Through the theoretical calculation and experiment analysis of the ultimate bearing capacity of the beam，furthermore，it was compared the beams of 3 different spans with other types of beams，the influential parameters on the ultimate capacity such as the thickness of steel sheet，the grade of concrete，the number of steel strand，the location of separator etc． were researched，which demonstrate that the longer the span，the advantage of this composite beam in ultimate capacity and deflection． As a result，it was suggested that the proposed prestressed steel box-concrete composite beam should be used in the house and bridge structure whose span is longer than 12 m．