This paper presents a method for estimating the vehicle structural weight in the conceptual design phases of reusable launch vehicles and analyzes the sensitivity of the multi-factors which affect the structural weight. The method is an application of liner regression analytic methods. Based on the analysis about the statistical data of the overall parameters of the vehicles, the estimating formulas of the structural weight for the vehicles are deduced using the method. By defining a sensitivity function and a sensitivity factor with dimensionless, the sensitivity of the estimating formulas to every overall parameter is analyzed. Numerical examples and the sensitivity tests indicate that those estimating formulas are available and practicable, and that wing aspect ratio, trapezoidal wing area, fuselage structural depth, vertical tail area and tail length are the most important factors that greatly affect the structural weight.