The innovative coaxial cable Bragg grating (CCBG) sensor not only achieves the attractive attributes of high resolution, remote operation and multiplexing capability, but also has the advantages of large strain capability and robustness to survive harsh conditions, suitable for structural health monitoring (SHM). The Q-factor of the resonances in CCBG is studied in this paper by coupled mode theory (CMT), to obtain a better understanding of the device physics. The relationships between geometrical parameters and the Q-factor are investigated quantitatively and closed-from expressions are obtained. Design guidelines are developed to improve the Q-factor and consequently improve the senor sensitivity and accuracy.