A large multi-HVDC infeeded receiving power network is being formed in Guangdong with the strategic plan“west-to-east power transmission” being implemented. Optimal planning is in urgent need to furthest meet the demand of dynamic voltage stability of the receiving network with the finite investment. The voltage collapse loss is evaluated based on risk assessment theory and post-contingency state transition analysis， by which economic assessment for security benefit of dynamic voltage support can be realized. A new model of dynamic voltage support optimization for receiving networks is then presented， in which the objective function is set to maximize the annual average benefit while meeting constraints in various conditions. Finally through the static load margin analysis and dynamic simulation on Guangdong power grid， the validity of the model proposed is proved and demonstrated.