Thyristor failure event occurred after Ultra HVDC island commissioning on April 23, 2012. This paper analyzes the reason of thyristor failure, introduces the process of the emergency shutdown and block of controlling and protection, and points out the controlling and protection logic problems. The logic optimization solutions are proposed and EMTDC and RTDS simulations are carried out. Simulation results verify the validity and correctness after the optimization of bypass switch closing. Optimization program has been widely implemented in the Yun-Guang and Nuozhadu Ultra HVDC controlling and protection system. The optimization scheme has played an active role in the end of project commissioning process, and the thyristor failure caused by the island bipolar block test never occurred.