Abstract: One-dimensional beam FEM method was previously used to predict the ship vibration level, but the precision droped greatly upwards four nodes, for the hull shear deformation was greatly effected at high orders. The results of 3D space FEM model calculation were proved more accurate, but it consumed too much work. It was valuable to improve one-dimensional beam method. Hull vibration frequencies of 3 ships were calculated with both one-dimensional beam FEM method and 3D FEM methods. The results were compared and improvement to one-dimensional beam FEM method was provided. 110 000 t oil tanker was used to prove that improvement. The shear lag coefficient was used in one-dimensional FEM method; 3D space FEM model of the whole ship was established in ANSYS software. It was proved that the modified one-dimensional FEM method was valid for 110 000 t oil tanker. It was valuable to predict hull frequency quickly and more accurately.