Abstract: This article takes the DC isolation switch， the main electrical equipment of a certain ultra-high voltage converter station project， as an example to study and compare the simulation tests of the DC isolation switch and its auxiliary equipment on the engineering site and in the factory. By conducting simulation experiments， theoretical calculations， and data organization in the factory， the results are compared with the actual operating conditions on site to identify the reasons for the differences， and the results meet the conditions. This provides a reference for the factory testing and on-site use of the main equipment in subsequent ultra-high voltage projects， while continuously improving the equipment installation quality level and overall construction efficiency on the project site.