Abstract: Carbon fiber reinforced polymer (CFRP) is a new material widely used in the field of vehicle lightweight design. However, the emission of a large amount of acid causes the CFRP operational environment to become acidic. The water absorption test of CFRP in an acid environment was carried out to analyze the effects of unidirectional ply angle, structural size, and solution pH on the water absorption characteristics of CFRP. The results showed that when the total amount of fibers and matrix is constant, arranging the fibers along the vertical long-axis direction increases the matrix content. This promotion of water absorption exceeds the barrier effect of the fibers, enhancing the material's water absorption behavior.It is also found that the influence of the interface on the water absorption process of CFRP cannot be ignored. When the specific surface area of the material is too large, it produces an edge effect, resulting in the acid-thermal water absorption diffusion coefficient along the thickness direction being greater than those in the length and width directions, leading to enhanced water absorption. A strongly acidic environment will lead to higher water absorption diffusion coefficients and saturated water absorption rate, It was also found that aging of CFRP in a strong acidic environment leads to an increase in tensile strength and a decrease in compressive strength. The results of this study can be used to guide the design and operational of CFRP bodies in real service environments to improve their service life in acidic environments.