The properties of light guiding mechanism and modes relating to the core refractive index in a hybrid photonic crystal fiber (PCF) are numerically investigated by the full-vectorial finite element method. The light guiding mechanism of core mode is the double-bandgap-guiding when the core refractive index is smaller than the effective index of the air-hole cladding in the hybrid-PCF. If the core refractive index is between the refractive indexes of the two kinds of hybrid-claddings, there is a co-operative action of the index-guiding and the bandgap-guiding on the guide mode in the core. Only the total internal reflection guiding occurs in the fiber when the core refractive index is greater than the effective index of the high-index rod cladding. Comparison of these guiding properties in the hybrid-PCF are also carried out. The results provide guidance for the design of hybrid photonic crystal fiber for special purposes.