A novel symmetric core cladding structure photonic crystal fiber(PCF) is proposed in the paper.The cross-section is composed of two groups of core cladding structures,which are completely symmetrical along the center of the section.All the air holes of a group of core cladding structures were filled with ethanol liquid,and the mode coupling properties between two cores are modulated by using the temperature sensitivity of the refractive index of the filled liquid.The mode coupling characteristics of the proposed PCF under different structure parameters and different temperature range from -20 ℃ to 70 ℃ are numerically investigated by using the full-vector finite element method.The calculations show that the mode coupling between the two cores is highly sensitive to temperature and has a very short coupling length,which is only 55.00 μm at the wavelength of 1550 nm,and the polarization splitting characteristics of short length and high extinction ratio can be realized,which can reach 84.45 dB with a length of 198 μm the proposed PCF at the wavelength of 1550 nm.The proposed PCF can be used to make temperature sensor and polarization beam splitter.