On-load tap changer(OLTC) is one of the most important components of converter transformer. Due to the complex operating conditions and increasing capacity of converter transformers, the switching process and type-selection technology of OLTC of converter transformer are different from those of ordinary power transformer. Taking the typical dual-resistance tap changer as an example, this paper introduces its switching principle, switching process simulations are carried on OLTC which is equipped on power transformer and converter transformer, the particularity of OLTC operation condition of the converter transformer is revealed. The analytical formulas of the recovery voltage of main and auxiliary contacts during the switching process of OLTC are derived, and they are compared with the simulation results. A type-selection technology of OLTC combined with the qualitative waveform simulation and the quantitative key parameter calculation is put forward, which provides reference and guiding significance for the design, type-selection and operation maintenance of OLTC of the converter transformer in the actual HVDC projects.