Abstract: In the solidification process of steel, the cooling rate is a very important parameter, and the cooling rate has a significant effect on the phase transformation of steel. In this study, the peritectic transformation temperature of 3.52%Al δ-TRIP (Transformation Induced Plasticity) Steel under different cooling rates was studied by Differential Scanning Calorimetry (DSC), the segregation degree of each element in δ-TRIP steel was analyzed by the Ohnaka model. The results show that with the increase of cooling rate from 10, 30 to 50 ℃·min-1, the liquidus temperature of δ-TRIP steel decreases, the solidus temperature first decreases and then increases, the enthalpy of L→L+δ phase transformation decreases with the increase of cooling rate, and the enthalpy of peritectic phase transformation first decreases and then increases with the increase of cooling rate. Among the six elements of δ-TRIP steel, the cooling rate has little effect on the segregation of C, Mn and S, and the cooling rate has a great effect on the segregation of Si, P and Al, which increases with the increase of cooling rate. The larger the cooling rate is, the more serious the segregation of Al element is. The solute enrichment of Al element will promote the formation of ferrite and inhibit the formation of austenite, so as to delay the process of peritectic reaction. The peritectic reaction temperature range is the crack sensitive area, which will increase the probability of crack generation.