In order to provide more safety for high speed vehicles entering in highway bridges, modern highways should be as aligned as possible with the overrun bridges. This obligation results in construction more skew bridges all over the world. In skew bridge the center line of the longitudinal deck elements are not perpendicular to abutment. The angle between center line of the deck and the line normal to abutment is called skew angle. In the traditional bridge designing methods, traffic loads are considered as static loads which are increased by the application of dynamic allowance factor. In current standards, the dynamic allowance factor is only function of span length or first natural frequency of the bridge. In this research dynamic response of a skew bridge under dynamic load using finite strip method based on Kirchhoff assumptions has been studied. The bridge deck is modeled as a thin plate and also for dynamic loads three models: Moving load, moving mass and moving vehicle, are taken into account. Effects of skew angle, natural frequency of the bridge, span length, loading speed, velocity parameter, loading model and load combinations on the response and the dynamic allowance factor of displacement and moment are studied. The results show that the dynamic allowance factor is not only the function of span length but also it highly depends on velocity, eccentricity, loading model and geometric characteristics of the bridge deck like skew angle.