First-principles calculations were performed to study the hydrogen bond in the camphorsulfonic (CSA) acid-doped polyaniline system. The density functional theory (DFT) method was used to calculate the ground-state geometric structure optimization. Meanwhile, the electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states were investigated by the time-dependent density functional theory (TDDFT) method. In the acid-doped system, SO⋯H–N type intermolecular hydrogen bonds were formed. The band lengths at the hydrogen bond formation point were elongated, and the stronger hydrogen-bond interaction causes longer bond stretching. DPA–DMSO was photoexcited to the S2 state which possessed the largest oscillator strength, and the ICPA–DMSO was photoexcited to the S3 state in a similar way. In addition, we also discussed the frontier molecular orbitals and the electron density transition.