We propose and experimentally demonstrate a demodulation technique for real-time monitoring the change process of liquid concentration based on a tilted fiber Bragg grating (TFBG) and differential amplification detection. Continuous variations of the TFBG transmission power are measured by using two photodiodes (or a precision reference voltage generator instead of the referenced photodiode) along with two integrated operational amplifier circuits (IOAC). The voltage-concentration curves are obtained, by recording the output voltages of the two IOACs at different time. The experimental results show that such a fast demodulation technique is capable of measuring the effective glycerol solution concentration over the range of about 89%~69%.