Photoacoustic tomography imaging (PAT) is a novel, non-ionizing and non-invasive imaging technology which is based on photoacoustic effect. PAT is a hybrid imaging technology combining pure optical imaging technology with ultrasonic detection technology, so it possesses high optical absorption contrast and ultrasound resolution. This emerging imaging technology has very broad application prospects in biomedical detection. The theory of photoacoustic tomography imaging is introduced. Comparison is made among different system structures and their advantages and disadvantages. Furthermore, the main detection objects of the various system, are introduced. Finally, we predict the trend of photoacoustic tomography imaging systems, and discuss the method to improve system performance parameters of PAT.