Based on tunable diode laser absorption spectroscopy (TDLAS) technique, an acetylene (C2H2) online detection system was developed by using the absorption band at the wavelength of 1.534 μm of C2H2 molecule. The sensing system consists of four modules including a distributed feedback (DFB) laser, a DFB laser driver, a gas cell with single optical path and a data processing module. With the prepared standard C2H2 gas sample, detailed measurements were carried out to study the detection performance of the system. Experimental results reveal that, the limit of the system (LOD) is about 0.02%; a good linear relationship is observed between C2H2 gas concentration and the amplitude of the 2f signal is within the range of 0.02%~1%. A long-term measurement lasting for 20 h on a 0.5% C2H2 gas sample was carried out to test the stability of the system. Compared with the C2H2 detection systems utilizing quantum cascaded lasers (QCLs) and wideband incandescence, this system has great advantage due to the capability of using long-distance and low-loss optical fiber for remote monitoring. With self-developed DFB laser driver and lock-in amplifier, the system has good prospects in industrial field because of its simple structure, low price and capability of easy to be integrated.