Abstract: HPR1000 (Hualong No.1) was developed upon over 30 years of pressurized water reactor (PWR) R&D experience of CNNC. It has fully absorbed the advanced design philosophy of GENⅢ nuclear power and the overall engineering experiences including design, construction, testing and operating among China’s current PWR fleet. HPR1000 satisfies the 1 000 MWe power level GENⅢ technical specifications with the 0.3g seismic resistance capability. In order to reach this capability, several key technologies were developed including structural reinforcement of key equipment, leakbeforebreak (LBB) application on piping, refined calculation of reactor coolant system (RCS) load distribution, standard seismic resistance design practice and safety margin evaluation. Upon these technologies, a set of seismic resistance improvement strategy was devised that guides the accomplishment of RCS seismic resistance evaluation and optimization. The technologies reported in this paper are applied in successive Hualong projects. Short descriptions of abovementioned key technologies that leads to successful seismic resistance design are presented herein: 1) Structural reinforcement are adopted at key locations to enable improved functional requirement, such as the enlarged nozzle diameter and wall thickness of reactor pressure vessel, and such improvement also facilitates stronger structural integrity upon resisting dynamical loadings; 2) The utilization of LBB technology on RCS main pipe and the surge pipe alleviates the load considerations under the loss of coolant accident (LOCA), which is usually considered in conjunction with safe shutdown earthquake (SSE) load for GENⅡ nuclear power plant RCS structural analyses, and the introduction of LBB thus greatly reduces the conservatism on RCS mechanical analysis; 3) The load distribution modeling and computation. Multifidelity load calculation modeling strategy is adopted in this study to enable the capture of main dynamical responses at different resolutions. Interfacial loading data are exchanged across each level for quick iterations of structural design and optimization; 4) Standardization of seismic environment. This is achieved via comparative study of seismic response spectrum among a set of representative rock conditions. Envelop spectrum is proposed herein with adequate conservatism that will be used for future plant design; 5) Safety margin analysis (SMA). The essence of SMA is to estimate the potential of seismic resistance on key components in RCS. SMA is a key part of plant probability safety analysis (PSA) procedure. High confidence low probability failure (HCLPF) is used to quantify how much margin a component may have. Such information is helpful on learning the overall capability of resisting earthquake of the entire RCS. Moreover, SMA results reveal the vulnerability of RCS components.