A general analysis method of curved bridge, pure twist theory, which is based on the bar structure mechanical, has been introduced in this paper, by analyzing the basic assumptions of the theory, the limitations of application of the theory is indicated, while the ratio between the width and span of the curved bridge is out of the rang prescribed in the theory. The prestress effect is studied by the method of numerical simulation based on the finite element software ANSYS . According to the result, it can be indicated that, under the prestress, a horizontal and vertical displacement of the curved beam have occurred. The whole beam appears the tendency of turning outside, and there has been wavy distortion in the outer cantilever slab of the box girder along the span. The analysis result shows that, the method of the force analysis of spatial entities should be adopted when the ratio of width/span is small, and the difference between the inner vertical resistant reaction and the outer one caused by the prestressing force should not be ignored.