The circular birefringence effect in the low birefringent photonic crystal fiber caused by fiber twist is investigated,which is applied in the Sagnac interferometer structure to realize a twist sensor.The mechanical force is applied on the photonic crystal fiber in the Sagnac loop to introduce initial linear birefringence and to generate a sinusoidal interference spectrum.Then,the dip wavelength of the spectrum shifts due to extra circular birefringence caused by the fiber twist.The relationship between the dip wavelength and twist angle follows Sinc function,which is in coincidence with the therical analysis.The achieved sensitivity and resolution of the sensor are 1.00 nm/(°) and 0.01°,respectively.The sensor possesses ultralow temperature coefficients of －0.5 pm/℃.