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ABSTRACT Coastal flooding caused by sea-level rise and storm surge is serious due to global extreme weather. The large-span floating sector gate (LSFSG) is important storm surge barrier to safeguard coastal-cities. A novel LSFSG was proposed, and the optimal design of LSFSG was achieved based on the structural stability and Multi-island genetic algorithm (MIGA). Finite element numerical simulations were conducted to show that the LSFSG with bio-inspired branching arms is optimal type under the constraints of structural strength, stiffness and stability, with a enlargement in structural bearing capacity by approximately 58%. The study may provide a valuable suggestion for structural design. INTRODUCTION With the warming of the global climate and the frequent occurrence of extreme weather, the average temperature of the sea and land surface has gradually increased (Hunt, 2013) and the sea level has gradually increased (Church et al., 2013) . Natural disasters such as storm surges have occurred frequently and intensified in coastal areas (Lin et al., 2012).The combined effects of these disasters have led to an increase in global sea level extremes (Muis et al., 2017; Vousdoukas et al., 2016), which seriously threatened the safety of urban residents in low-lying coastal areas, Annual direct natural disasters and disaster chains cause huge population mortality and socioeconomic losses in coastal areas (Pears et al., 2016; Wahl et al., 2017; Kulp et al., 2019). Flood control projects can protect coastal areas. Compared with the traditional barrage project, the storm surge barrier is the strongest control function and the most economical and beautiful choice, which can effectively reduce flood inundation losses caused by natural disasters such as storm surges in the estuary delta. Storm surge barrier is an important part of flood protection system in coastal cities (Witzeet al.,2018; van Berchum et al., 2019; Kluijver et al., 2019; Rasmussen et al., 2020). Storm surge barrier is a kind of movable water gate, which is used to protect coastal cities from coastal floods caused by natural disasters such as storm surges (Samyn et al., 2007; Mooyaart et al., 2017; Xu et al., 2018). The large-span floating sector gate (LSFSG) consists of two horizontal rotating radial gate, which bears water load in both directions and meets the two requirements of fast tide flood protection and navigation. In addition, It is widely used in urban flood control projects with long spans and low heads (Hill, 2012). Maeslantkering used this gate at the first time at New Waterway in Rotterdam, Netherlands (Kolkman et al., 2007; Rijkswaterstaat, 2012). The gate arm is a triangular lattice truss structure, and the gate body is an Lshaped box structure, it's show in Fig.1. The gate operation method uses the ballast system to fill and pump water into the gate body to achieve the sinking and floating of the gate body structure, making full use of the buoyancy and self-weight of the water body.