Abstract: Planetary gear trains are widely used in industry due to their unique advantages,such as compact volume and high load capability etc,over other kinds of transmissions.In the past years,several mathematical models for the elasto dynamics have been developed for different purposes.In this paper,the models used in elasto dynamics of planetary trains are discussed and a classification of the models is made.The algorithms frequently utilized to search for the response of the system are also outlined.Some aspects relating to dynamics of planetary gear trains,such as vibration mode shape,load sharing and vibration control are discussed.Finally some important problems deserving more efforts to study in the future are pointed out.