In order to meet the special needs of helicopters with sufficient operating time for landing safely under loss-of-lubrication conditions, it is necessary to avoid the scuffing failure and predict the operating time. A spur gear is taken as the research object. Considering the change of moving source of heat on the gear, simplified models are adopted. Both the spatial distribution and the time history of the gear temperature are simulated by finite element method. The simulation results of bulk temperature are compared with the test measurement ones, while those of the flash temperature history are compared with the experimental and calculation results by Blok flash temperature formula, respectively. The comparison shows a good agreement. The results of simulation and comparison are discussed.