Abstract: In order to eliminate the bamboo joint phenomenon in the drawing process of packaging wire steel, reduce the influence of hard phase structure and improve the uniformity of structure, the phase transformation of packaging wire steel under different cooling rates was studied by thermal simulation machine, and the continuous cooling transformation curves were drawn combined with the microstructure morphology.The results show that the size of ferrite and pearlite decreases with the increase of cooling rate after thermal deformation, but the decreasing trend is gradually weakened, especially when the cooling rate is greater than 5 ℃/s, the size of ferrite and pearlite changes little. Through statistical fitting of data, when the cooling rate is less than 30 ℃/s, the relationship between ferrite grain size d and cooling rate v during continuous cooling of packaging wire steel is established, and the expression is d=35.56+6.59 ln(1/v).