The invention discloses a regional power grid reactive power optimization method relating to a flexible HVDC system. The method achieves the purpose of regional reactive power optimization on the flexible HVDC AC and DC parallel system and provides a basis for setting reactive power control reference values for a current converter. The method includes the steps of acquiring basic parameters of a power grid, determining a relational expression of voltage, current and power of the flexible HVDC system, establishing a reactive power optimization objective function with power regulation cost of flexible HVDC considered, determining equality and inequality constraints of corresponding variables according to the variables in the objective function, solving the regional power grid reactive power optimization objective function with the genetic algorithm by considering current constraints of the current converter of the flexible HVDC system under different operation modes, and improving power control strategies according to current converter reactive current optimal solutions obtained by optimal computation. According to the method, the active power regulation cost of flexible HVDC and the current constraints of the current converter are considered, and therefore rationality in setting the reactive power control reference values of the current converter is improved.