Its biquadratic finite element approximation is considered and under the appropriately graded meshes, quasi-optimal orde然后，考虑此方程在分层网格剖分上的双二次有限元逼近，在ε-加权H^1-模意义下得到了至多相差一个关于摄动参数对数因子的拟最优阶收敛的误差估计。