Abstract: In order to study dynamical bucking and bifurcations of an elastic beam, we establish nonlinear Mathieu equation of this beam and discuss thoroughly the characteristic of 3/2 subharmonic bifurcation in parametrically excited system. Our studies show that researchers only got bifurcating characteristic of a degenerate case when they investigated these problems. We analyse influence of truncation in bifurcating equation on bifurcation set, and obtain some new results. Finally, we give result of experiment on ...