The strength and stiffness of 4300 rolling mill housing affect the quality of plate much. In presented research a problem that belongs to the stresses, deformations and modal analysis topic was investigated. The finite element method (FEM) and the electrical measuring method were used for the investigation. Modeling, meshing, loading and analysis on the housing are finished by Pro/E and Ansys 10.0. The dangerous point locates on the chamfer of upright and low carriage. The FEM results are larger than those of measuring by comparison. Natural frequencies and main vibration modes of the housing from first to fifteenth step are found. The dynamic bending and twisting deformation are the main factors which affect the dynamic characters of rolling mill. The middle of upright is the weakest position. The results of this article supply the basis for understanding the working state, maintenance and design of the 4300 rolling mill housing.