Abstract: In this paper the author makes use of the principle of virtual displacement and the cubic B-spline function as a piecewise function to analyze free vibration of orthotropic plate bridge. The author derives a computational scheme well suited for various boundary conditions for the orthotropic plate and plate-beam structures on rectangular region. The main prominent features of this method are more accurate and more economic in computing storage and time requirement. It is easily carried out with a medium-sized or small-sized computer.