Abstract: The rattling model of a one stage gear system was established,in which mass unbalance,speed fluctuation of driving shaft and backlash of the gear pair were considered.Its governing equations represent a mapping system.By means of numerical simulation,three rattling conditions were researched:(1) speed fluctuation exists only;(2) mass unbalance exists only;(3) both coexist.According to the calculation results,at different inspiring factors and amplitudes,there are different rattling dynamic characteristics,for example,one period,multiple period and quasi period.The rattling resulting from speed fluctuation is different from that resulting from mass unbalance.The rattling characteristics resulting from both simultaneously are different fro-m overlapped characteristics resulting from both individually.It is more reasonable that the factors of speed and mass unbalance are taken together to investigate the rattling dynamics of a gear system.