Abstract: The last circuit breaker protection is used for preventing the adverse effect on equipment caused by severe over-voltage when all the AC loads in the inverter side are shedding. In addition to conventional last circuit breaker protection, UHVDC convertor station is also equipped with arrester based last circuit breaker protection as backup protection. However, problem also exists on arrester based last circuit breaker protection for its adaptability of action speed under different over-voltage factors. To cover the deficiency of the existing method, firstly, instead of constant, the power integration of arrest was obtained by using real-time voltage, which form an improved arrest-based last circuit breaker protection. Besides, in order to improve the performance of the protection, a dynamic setting strategy of threshold based on the inverse characteristic of voltage and energy was proposed. Secondly, an UHVDC simulation model was established according to the actual parameters of Xiangjiaba-Shanghai UHVDC transmission system, which meet the demand of research. A series of simulation examples show that the improved method can shorten the duration time of equipment withstanding severe over-voltage under the premise of guaranteed operating reliability, which can protect the equipment in safe.