Abstract: Aiming at the problem of difficult parameter tuning of sliding mode variable control for back-to-back MMC-HVDC grid connected composite device, a controller optimization method based on improved moth-flame optimization algorithm is proposed. Good point set initialization is introduced to increase the diversity of variable values when initializing the population, speed up the convergence speed of the algorithm and reduce the amount of calculation. Combined with Lévy flight update mechanism, the algorithm can avoid falling into local optimization. The performance of the proposed improved moth-flame optimization algorithm is tested by 8 standard test functions, and compared with several common swarm intelligence optimization algorithms to verify the superiority of the proposed algorithm. The Python-PSCAD joint simulation method is studied and realized. Taking the comprehensive ITAE index as the objective function, the parameters of the sliding mode variable controller are optimized. The simulation results show that the controller parameters optimized by the improved moth-flame optimization algorithm can make the grid connected composite device have better dynamic performance.