Using T800 grade carbon fiber/epoxy resin unidirectional tape automatic laying prepreg, test laminates with different thinkness were manufactured by automatic fiber placement process. The effects of curing pressure, laminate thinkness and size, automatic fiber placement pressure and other parameters on porosity and porosity distribution were investigated. Composites porosity intervals were characterized using ultrasonic C-scan. The results show that when the curing pressure drops to a certain critical point, the porosity increases rapidly first and then slows down gradually; Thicker laminates have higher porosity than thinner laminates, and there are more pores near the middle and bottom of the ply; For laminaters with a larger size, the areas with high porosity are relatively concentrated near the middle of the laminates, and the porosity interval is large; When the curing pressure is low, the laminates laid with a small laying pressures will form a higher porosity; For large and complex composites structures, the influence of different automatic fiber placement parameters on porosity also has the above trend.