Abstract: Acoustic emission(AE) technique has been widely applied to pressure vessel and piping inspection. Sound source location analysis plays an important role in the whole AE inspection and evaluation process, how to improve the location precision to an extent is the research focus all over the world. For AE sound source location of pressure vessel and piping, the arrival-time difference location method is mainly used, i.e. compute arrival-time difference which sound source signals arrive at different sensors to determine the sound source location. If an active sound source is on the internal surface or in the wall not on the external surface of thick-wall pressure vessels, the location error obviously exists because of the wall thickness influence. Aiming at the problem, the sound source error for thick-wall pressure vessels is deduced in detail, the sound source location error formulas are founded and the change law of location error with the wall thickness is analyzed and discussed too. The results indicate that the location errors in the experiment are both in good agreement with those in theory with a maximum relative error of 7.12%. Furthermore, when the thickness is less than 600 mm, it is proposed that about 200 mm radius area around the source location should be rechecked by normal nondestructive testing methods to determine the actual source location by AE inspection.