As a key electric equipment for reactive power compensation and voltage support in new energy substations, high voltage cascaded STATCOM needs low-voltage ride-through (LVRT) capacity, especially under the asymmetrical fault of three-phase grid voltage. To solve this problem, this paper analyzes grid side and conversion chain side respectively by using symmetrical component method and deduces a mathematical formula. And based on the formula, a LVRT control strategy of high voltage cascaded STATCOM based on negative-sequence current injection is proposed. The proposed strategy includes control algorithm and control logics, which can satisfy voltage-drop under both three-phase symmetric and asymmetric grid. The validity of the method is verified by simulations and experiments, and it has been applied in engineering application.