When turning on a thyristor valve, the AC system current, stray capacitance current, damping branch current, valve arrester current, and other currents are coupled to each other, which determines the opening process of the thyristor together. When turning off a thyristor valve, the reverse recovery process, short-circuit impedance of transformer, and damping branch parameters determine the thyristor turn-off voltage together. Based on PSCAD/EMTCD, this paper builds a thyristor valve electromagnetic transient simulation model to study the influencing factors and time-varying mechanism of the voltage and current of switching process of thyristor valve. The result shows the saturation reactor and damping resistance play important roles in suppressing the open current of capacitor, and the short-circuit impedance has a greater effect on the commutation overshoot. Studying the influencing factors of the switching process of the thyristor valve has certain guiding significance for parameter selection and device design in engineering design.