In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly(3-octylthiophene)(P3OT) film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form I and form II crystal modifications of P3 OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form II, i.e. carbon disulfide(CS2) which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3 OT. Therefore, this finding provides an alternative way to obtain form II. By temperature dependent IR spectroscopy, the structural evolution of P3 OT during the form II to form I phase transition process has also been studied in detail. In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the covered dried poly (3-octylthiophene) (P3OT) film has been investigated by the combination of DSC, WAXD and FTIR techniques. is employed as the solvent, it was unexpectedly found that form I and form II crystal modifications of P3 OT could be respectively obtained room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form II, ie carbon disulfide (CS2 ) is which is toxic and corrosive and more suitable for solution processing of P3 OT. Thus, this finding provides an alternative way to obtain form II. By temperature dependent IR spectroscopy, the structural evolution of P3 OT during the form II to form I phase transition process has also been studied in detail.