The effective refractive index of finite one-dimensional photonic crystal (PC) was investigated.Firstly,the concept of a complex effective refractive index for the structure of finite periodic PC was introduced.Then the complex transmission coefficient was calculated by using the transfer matrix method.On this basis,analytical expression of the effective refractive index could be derived.Considered by the spatial structure of photonic crystal and the existence of photonic band-gap,the characteristics of photonic band-gap structure,the effective refractive index,optical thickness,physical thickness and the center wavelength were investigated.It is found that amplitude of oscillation for the effective refractive index can be effected by the ratio of refractive index of the basic periodic structure and the physical thickness of the basic periodic structure of PC; Center wavelength has no effect on the effective refractive index.