Abstract: Operation of the active direct-current vacuum circuit breaker (ADC-VCB) was mathematically modeled, theoretically analyzed and numerically simulated in Linear Decreasing Weight Particle Swarm Optimization (LDW-PSO) algorithm and in Monte Carlo method for design optimization of the commutation LC-circuit.The influence of the LC-circuit on the arc extinguishing ability and growth of post-arc sheath-layer was investigated.The (12 kV/10 kA) ADC-VCB, equipped with the optimized LC-circuit, was tested via Monte Carlo simulation.The simulated results show that the LC-circuit optimized in LDW-PSO algorithm is capable of ensuring reliable interruption of ADC-VCB.In addition, when it comes to optimization of LC-circuit of ADC-VCB, LDW-PSO algorithm outperforms the conventional PSO algorithm because of lower design cost.Experimental evaluation of the newly-designed ADC-VCB was underway and will be reported later.