Abstract: Analyzing the phenomenon and causes of transient temperature oscillation during the FEM solution to temperature field. The influences of different element meshing methods and time-step on the transient temperature oscillation were discussed. Refining the elements and S-type time-variable steps were proposed. The calculation results showed that refining the elements layer upon layer not only restrains the transient temperature oscillation so as to come to the required calculation accuracy but also reduces the calculating time. Compared to the fixed steps, the S-type time-variable steps can shorten more than 10 times the calculating time with the oscillation restrained, accuracy ensured and other conditions kept constant. The results were theoretically and practically important to improve calculation accuracy and expedite calculation speed.