Taking a large tower of horizontal-axis wind turbine as an example, the factors affecting horizontal-axis wind turbine tower are analyzed by the test of four factors and three levels, the modals are calculated using matrix analysis. The finite element model is built and the modal analysis is completed by using the finite element software of ABAQUS. The factors including bottom of the tower openings, the total mass of the cabin and wind wheel (with hubs), the overall eccentric of the cabin and wind wheel (with hubs), and the wall thickness and diameter of the tower are considered in the modal analysis. Through the research of the factors on horizontal-axis wind turbine tower, the results show that the significant factors are the total mass of the cabin and wind wheel (with hubs), and the wall thickness and diameter of the tower, however the factor of the bottom of the tower openings could be ignored; the impact of the overall eccentric of the cabin and wind wheel (with hubs) on horizontal-axis wind turbine tower is determined by the degree of the overall eccentric of the cabin and wind wheel (with hubs), the bigger bias is, the bigger affected degree is.