Photo-induced absorption in poly (bis (p-toluene sulphonate) ester of 2,4-hexadiyne-1, 6-diol) (PDA-TS) single crystal is studied theoretically. A mechanism of photo-induced absor-ption is proposed as exciton excitation. The binding energies for single and triple excitons are calculated and the photo-induced absorption peak at 1.35eV is considered as resulting from the transition 3Ag→3Bu. This agrees with experimental data.