Traditional electromagnetic transient simulations use a detailed model to model the voltage source converter （VSC） and use the double interpolation method （DIM） to handle switching events within a step. Due to the time-varying conductor array of the detailed model and the complex DIM algorithm process, the computational efficiency is seriously affected when performing large grid simulations. To address this issue, the semi-implicit delay decoupling principle is applied to model VSC and the handling of switching events within a step is investigated to improve the simulation efficiency by equating the duty cycle of the switching function within a step instead of DIM. Firstly, starting from the state equation of VSC, the decoupling model of VSC is obtained to realise the parallel computation of the converter and improve the computational efficiency. Secondly, the mechanism for generating the accumulated error when switching events are not processed is analyzed, and the computational time scale and the calculation of the equivalent duty cycle of the switching function is also given to ensure the simulation accuracy. Finally, the accuracy and effectiveness of the proposed method are verified by the simulation waveforms of PSCAD as a benchmark, and the methodological features of the proposed method are discussed.