Loss characteristics of antiresonant reflecting plastic optical fiber with cobweb structural cladding and its relationships with the structural parameters are analyzed in the wavelength 1.3 μm. The cladding of this optical fiber is equivalent to periodical multilayer films and numerically simulated by asymptotic transfer matrix method. The effects of the number of alternating layers N, the thickness of highindex layer d2 and index contrast n2∶n1 on the loss characteristics are analyzed to optimize the structural parameters. The numerical simulation results show that the mode loss decreases rapidly in the first and reaches a fixed value in the last as the N increases; the mode lesses increase linearly as the d2 increases; the larger the n2∶n1, the lower the loss at the anti resonant wavelength. On that basis, the thickness of the air layers d1 and the radius of the hollow core rco are optimized by simulated annealing optimization algorithm. Finally, by using above optimal combination of the structural parameters N3, d2=2.648 μm, n2∶n1=1.49∶1.0, d1=3 μm and rco=100 μm, the lowest loss calsulated is 0.449 dB/km。