The integration of a high proportion of renewable energy and a large number of pieces of power electronic equipment represented by wind power, energy storage, and VSC-HVDC transmission has reduced the proportion of traditional thermal power in the grid. This will affect the frequency stability of the power system. In order to quantitatively analyze the frequency characteristics of the power system under the joint frequency modulation of wind power, energy storage, and VSC-HVDC systems, this paper first proposes the overall idea of quantitative analysis of the grid frequency characteristics in these circumstances and establishes a wind power-energy storage-flexible HVDC transmission joint frequency modulation frequency response model. Second, based on a frequency characteristic transfer function, this paper theoretically deduces the steady-state frequency error, the initial frequency change rate, the maximum frequency deviation and the frequency safety margin of the power system. Then it quantitatively analyzes the variation law of steady-state frequency error and the influence of the inertia time constant and auxiliary frequency modulation unit control proportional coefficient on frequency stability, and calculates the relationship between steady-state frequency error and power disturbance. Finally, the feasibility and effectiveness of the analysis method proposed are verified by simulation software. The simulation shows that the method proposed can effectively and quantitatively analyze the frequency characteristics of the power system, and can provide guidance for the safe and stable operation and control of the frequency of the power grid for a power system with a large amount of renewables and number of power electronics.