Hot compression tests were performed on gleeble-3800 thermal simulation machine to study the effect of different deformation parameters on microstructure of non-quenched and tempered steel with ferrite and pearlite.The results show that low deformation temperature can increase the content of ferrite.Increasing the degree of deformation has significant effect on grain refinement.Because large deformation can enhance the degree of fragmentation of grains,promote nucleation of eutectoid ferrite precipitate and increase the ferrite content,and non-quenched and tempered steel toughness is increased.High cooling speed can refine ferrite size and decrease the pearlite spacing significantly.In the temperature range of phase transition,slow cooling after rapid cooling can reduce the average size of pearlite and improve the toughness of the microstructure remarkably.