An optimal placement method for dynamic reactive power compensation devices is proposed in this paper to improve the immunity to commutation failures in multi-infeed HVDC systems. An electromagnetic transient simulation-based approach for computing the commutation failure immunity index is presented. An identification method is proposed for localizing zones in the receiving end power system where a fault will trigger simultaneous commutation failures of multiple HVDC infeeds. Various types of dynamic reactive power compensation devices are compared in their performance of improving commutation failure immunity. Finally, the optimal placement plan for dynamic reactive power compensation devices are to be made. Simulation results of New England 39-bus system verify the effectiveness of the proposed optimal placement method.