The invention provides a method and device for determining the dynamic equivalent conicity of a railway vehicle, and relates to the technical field of railway vehicle routes. The method comprises the steps that tread data of each wheel in a wheel tread library and profile data of each steel rail in a steel rail profile library are classified and combined respectively, and various wheel-rail molded surface combined working conditions are formed; the change curve of the equivalent conicity corresponding to the wheel-rail molded surface combined working conditions along with the gauge is determined; the tread data of each wheel and the profile data of each steel rail are matched with the wheel-rail molded surface combined working conditions, and the wheel-rail molded surface combined working conditions corresponding to actual operation of the railway vehicle are determined; the actually measured gauge of a route is obtained, the dynamic equivalent conicity corresponding to the actually measured rail gauge on each mileage point is determined according to the change curve of the dynamic equivalent conicity along with the gauge, and the dynamic equivalent conicity of the railway vehicle on the whole route is formed.