A novel temperature sensor based on a symmetric core cladding structure photonic crystal fiber (PCF) is proposed. Circular air holes arranged in square-lattice are completely symmetrical along the cross-section center of the proposed PCF. Two solid fiber cores are formed by separately removed two air holes of the cross-section center of the proposed PCF,and one side of the symmetrical cladding air holes are filled by the ethanol liquid. The mode coupling of the double-core of the proposed PCF is modulated by the change of the refractive index of the filling liquid which is caused by the change of temperature. The temperature characteristics of a 1 cm PCF under different temperature range from 20~25 ℃ are numerically investigated by using the full-vector finite element method. The calculations show that a very high temperature sensitivity of 3.21 nm/℃ could be achieved.