The invention discloses a dynamic reactive supporting capability evaluation method and system considering continuous phase commutation failure. The method comprises the steps of: screening out effective reactive compensation equipment according to the reactive sensitivity of of an extra-high voltage DC convertor station bus voltage on all kinds of reactive compensation equipment, and performing statistics on an inductive reactive adjustment space for capacitor devices; adjust grid operation mode based on the reactive adjustment space of effective reactance equipment; adjusting a power grid operation mode according to the reactive adjustment amount of each gear, performing time domain simulation for a short circuit fault of an AC line of a converter station outgoing line, and determining acritical power grid operation mode of continuous phase commutation failure; and calculating a dynamic reactive reserve factor based on the reactive variation and the sensitivity of the dynamic reactive compensation equipment and the power of an extra-high voltage DC system. By adopting the dynamic reactive supporting capability evaluation method and system disclosed by the invention, boundary conditions for continuous phase commutation failure are accurately calculated, and the dynamic reactive supporting capability of the power grid is evaluated.