Glucose concentration is detected by using evanescent absorption method. Plastic optical fiber is used as sensor head and light transmit element. A high brightness blue LED modulated with sine signal is used as excitation source with spectrum centered at 470 nm. The sensitivity of the system under different shaped sensor heads (U-shaped, biconical-shaped, spiral-shaped) is measured, and the spiral-shaped sensor head shows the highest sensitivity to glucose. The relationship between the spiral-shaped output light power and glucose concentration is linearly and the linear coefficient is 0.986. The sensitivity of the sensor head is 0.1 μg/mL. The system shows excellent reversibility when the sensor is tested by alternately cycling between 0 mg/100 mL and 25 mg/100 mL glucose solution in five cycles.