The leaky spectrum of Photonic crystal fibers (PCF) was simulated with beam propagation method. The results showed that the leaky spectrum usually had several bandgaps,which would provide theoretical reference for designing a novel multi-band filter. Furthermore,the leaky spectrum was very sensitive to the PCF structure,the spectrum was affected not only by the period of the air hole but also by its dimension. Finally,the liquid crystal (LC) could be infiltrated in the air holes of the PCF,because the refractive index of LC could be tuned by controlling the voltage and the temperature. The peak leaky wavelength and bandgap wavelength would red shift with the LC refractive index increasing,which would provide reference for designing a novel tunable filter and optical switch by controlling the voltage or tune the LC temperature.