Conventional power supplies are replaced by DC system and local new energy gradually. Increasing the reactive power output of conventional power supply in advance will induce potential risk of steady state over voltage and the insufficient dynamic reactive power reserve. Therefore, a two-stage heuristic optimization method considering start-up measures is proposed to solve the transient voltage dip security preventive control model. In order to reduce the computing scale, faults are selected according to the weakest transient voltage bus and the measures are selected according to the performance-price ratio. The reactors/capacitors switching measures and reactive power adjustable units are searched with the reserved part of the reactive adjustable space. Then, the start-up unit measures and the balancing active power adjustable unit measures are searched if the transient voltage safety margin cannot be improved obviously. Combinatorial optimization and enumeration are adopted in parallel computation to improve computation efficiency. The effectiveness of the proposed method is verified by an example of an actual power grid.