Acoustic lens is applied in the research of photoacoustic imaging. The aberration is always inevitable due to the existence of the acoustic lens, and it influences the resolution of the imaging system severely. However, the imaging system based on an acoustic lens also provides a new method for observing the aberration of a system and testing the quality of the acoustic lens. In this paper, a method of observing the aberration of photoacoustic imaging system is reported, and the causes of aberrations are discussed based on the theory of lens aberration. All these would be helpful to correct the aberration and improve the resolving power of acoustic lens.