To further enhance the sensitivity of photonic crystal fiber (PCF), a novel PCF structure incorporating both circular and rectangular air holes is designed. The proposed configuration comprises a four-layer cladding with circular air holes and a core region embedded with five rectangular air holes. Utilizing the full-vector finite element method with perfectly matched layer (PML) boundary conditions, the optical properties of the PCF are systematically simulated and analyzed when infiltrated with three analytes: water, ethanol, and benzene. The results demonstrate that at the wavelength of 1.55 μm, the designed PCF achieves sensitivities of 71.8%, 74.5%, and 75.6% for the three analytes, representing improvements of 1.26~7.97 times, 1.24~6.2 times, and 1.2~5.6 times, respectively, compared to existing PCF. Furthermore, the structure exhibits high birefringence on the order of 10^-3 and ultralow confinement loss below 10^-5 dB/cm.