Abstract: A new effective way to formulate thin plate element can be realized by using the similarity theory between plane elasticity and plate bending. According to this theory, plane elasticity elements can be transformedinto plate bending ones. In this paper, starting with the 4-noded isoparametric element Q4, we present a newquadrilateral eight D.O.F(degree of freedom)bi-linear thin plate element on the basis of the similarity theory. The new plate bending element can be viewed as the simplest quadrilateral thin plate element. Numerical results for typical problems show that this new element can pass the patch test. It is independent of the orientation of the axesof coordinates and has a good convergence and a satisfactory precision. It is a low order thin plate element of high performance.