We used a piezoelectric ceramics as photoacoustic detector and investigated the dependence of photoacoustic signal on optical beam position at samples which was yielded by the optical absorption of the crystal Si at 10.6 /wn. The experimental results demonstrate that the photoacoustio signal was maximum when the optical beam was located at the centre of sample. When the optical beam scans along the diameter of the circular sample the photoacoustic signals decrease gradually as the distance between the position and the centre ’of sample increase. The measured results are in good agreement with those of the theoretical calculations.