Abstract In this paper, we proposed a new kind of quasi-37-cores fiber structure consisting of 15 conventional cores and 22 air-hole cores. Strict dual-mode condition is systematically analyzed about three structure parameters, core-to-core pitch, relative core diameter, and difference of refractive index between core and cladding. Large effective area about 1910.98 μ m 2 with low bending loss less than 10 − 3 dB / m is achieved while keeping strict dual-mode. This structured fiber has a great potential in high power fiber lasers and amplifiers.