By analyzing the modular multilevel converter (MMC) double star structure topology of cascaded half-bridge sub-modules, a static var generator topology of improved MMC containing gate turn-off thyristor (GTO) is proposed. Compared with topologies such as cascaded H-bridge static synchronous compensator (STATCOM), it only uses the lower half bridge-arm of the double-star MMC structure, and an H-bridge module is added to the upper layer of the lower half bridge-arm of the MMC structure. However, the H-bridge module requires to withstand higher voltage level in high-voltage scenarios. and has relatively low frequency requirements, so GTO is choosed to form the H-bridge circuit. The corresponding modulation and control strategy are designed for the circuit topology. Then, the improved MMC-STATCOM and the traditional cascaded H-bridge structure STATCOM are compared, the compensation current THD of this solution and the cascaded H-bridge are both less than 2% when the same cascaded modules are used, and the number of switching devices used in improved MMC-STATCOM is less. Finally, by comparing the reactive current command value with the reactive component of compensating current, the dynamic performance of the improved MMC-STATCOM in reactive power compensation and the effectiveness of the control scheme are verified.