The Beer-Lambert law, taking into account the pressure broadening of the absorption lines function is analyzed, then it is used for multi-point acetylene gas detection. A fiber optical multi-point acetylene sensing system using dense wavelength division multiplexers, which takes advantage of different absorption lines to tag different probes in the system, is put forward. This system is easy to build and operate, while it does not need to modulate the light source. In addition, the system has a much smaller system loss and cross talks as the consequences of employing the dense wavelength division multiplexers. Theoretical results show that the maximum sensor number of the system is eighteen with a 0.5% sensitivity using the absorption lines from 1510 to 1540 nm. A three-point sensing system is experimentally demonstrated and the errors of the measured results are within 1.8%.