In order to achieve blood glucose concentration detection with ultra-low sample volume and high sensitivity, the influence of the wall thickness and diameter of liquid-core microtube cavity(MTC) on whispery gallery mode(WGM) resonance property was analyzed based on finite-difference time-domain(FDTD) method. The MTC was fabricated by melt-taping method. High-precision coupling of MTC and tapered fiber and the excitation of WGM resonance spectrum were realized by high-precision electronically controlled displacement platform. The surface functionalization and over-coupling methods of MTC were carried out to improve sensitivity and stability. Theoretical analysis and experimental verification have been carried out. The experimental results show that the linearity and sensitivity of the surface functionalized liquid-core MTC sensor are 0.988 and 0.911pm/(mmol·L-1), respectively. The low-concentration blood glucose optical sensor has high sensitivity and stability. This result is helpful for real-time and rapid monitoring of blood sugar during training of athletes, and for ensuring the safety and durability of sports.