In response to the modern power grid with multiple HVDC injections, extractions, and flexible loads, this paper proposes a transient frequency coordination support method based on wide-area measurement technology. The method first linearizes the power increment equations for each node in the power grid, establishing a system state equation based on wide-area measurement data after disturbance. Then, using this equation, the paper constructs a frequency dynamic analysis model for the power grid, considering both HVDC power modulation and flexible load regulation. By taking into account the impact of different control schemes on the power flow safety, an optimization model for transient frequency coordination control is constructed. Finally, through solving the optimization model, the paper presents a transient frequency coordination support strategy for emergency situations involving both multiple HVDC power modulations and flexible load regulations. The proposed method is validated using the improved IEEE 50-generator system, and the results and control effects are compared and analyzed, demonstrating the correctness and effectiveness of the proposed approach.