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We investigate the propagation properties of a multi-layer photonic crystal fiber with novel rhombic air holes using the finite element method,and calculate the dependence of the propagation properties on the wavelength in the fiber with different geometrical structural parameters,including the inteal angle and the exteal arrangement of the rhombic air holes.Optimizing these parameters,we design a photonic crystal which exhibits both a small dispersion value and low loss near the wavelength of 1.55 μm.Photonic crystal fibers are known as microstructured optical fibers or multi-hole optical fibers,and their cross sections have periodic structures with hollows in the centers due to one or more missing air holes as shown in Fig.1.The light wave can propagate along this hollow structure,which can be considered as the core of the fiber.According to the light-guiding mechanism,there are two types of photonic crystal fibers:total inteal reflection photonic crystal fibers and photonic bandgap photonic crystal fibers.[1] The propagation properties of total inteal reflection photonic crystal fibers are determined by the arrangements of holes in the transverse field.[1,2] With the flexibility to control the arrangement,size and shape of the air holes,various photonic crystal fibers with different optical properties can be designed as desired.Recently the microstructural design of photonic crystal fibers has drawn extensive attention over the world.[3] As a novel kind of optical fiber,photonic crystal fibers have been widely used for optoelectronic devices.