The technology of photoacoustic spectrum has features of high sensitivity, continuous and fast in situ measurement in detecting acetylene in low concentration. A new wavelength modulated photoacoustic spectrometer based on a near-infrared tunable erbium doped fiber laser (TEDFL) and a high power erbium doped fiber amplifier (EDFA) is developed. This system is demonstrated with low concentration acetylene measurement at the 1530.37 nm transition line, by incorporation of a first-longitudinal resonant photoacoustic cell with double absorption optical path and lock-in harmonic detection technique, yielding a detection limit of 1.3×10-9 at room temperature and atmospheric pressure and this can meet the demands of acetylene detection and analysis in industry, environment monitoring and power system.