The photoacoustic spectroscopy technique of infrared radiation combined with a mechanical chopper has the disadvantages of high cost and easy introduction of correlated noise. In this paper, an electrically modulated pulsed infrared (EMPIR) light source is used instead of a mechanical chopper to realize the detection of methane, ethane and ethylene. A photoacoustic spectroscopy gas detection system based on the electrically modulated pulsed infrared light source is constructed, and a control test is carried out with the mechanical chopper modulation detection system to verify the effectiveness of the electrically modulated method in reducing the signal-to-noise ratio. The effects of the modulation frequency of the electrically modulated pulsed infrared light source and the duty cycle of the PWM signal on the detection signal-to-noise ratio were investigated, and the experimental results showed that under the condition that the air pressure inside the photoacoustic cavity was 0.1MPa, the maximum signal-to-noise ratio was achieved when the pulsed infrared light source was driven at a frequency of 30Hz and the duty cycle of the PWM signal was 70%. The lowest detection limits of methane, ethane and ethylene were 11.8μL/L, 4.74μL/L and 17.8μL/L, respectively, at three times of the signal-to-noise ratio. The reproducibility of the detection system was good, with the relative standard deviation (RSD) of less than 5%, and the accuracy of the modeling was verified by configuring the gas samples of two different concentrations with the error of no more than 15%.