Based on CSP technics, using Gleeble1500-D hot simulation machine, making the single, dual, multi-pass compression experiment of Q345B steel with rare earth Nd respectively, different deformation conditions influencing Q345B steel of recrystallization behavior and the microstructure evolution rule in the hot rolling process have been studied. The results show that: the single, dual-pass experiments of Q345B steel with rare earth Nd are according with general experimental rules. According to single, dual-pass results, we establish multi-pass compression project. In that project, the grain samples with rare earth element Nd are finer than others. It explains that appending rare earth Nd has the obvious function of refining grains. At the same time, the degree of refining grains is different in the different project. It explains that in order to obtain fine grains, we should choose feat technics. By contrast, we can educe that the grains are more fine and uniform in a project.