The oscillation phenomena for granular mixture within a vertically vibrated container are investigated with the event-driven method. The container consists of two rooms with equal size separated by a clapboard with certain height，and two kinds of granules with the radius of one twice as larger as the other are used. Investigation results indicate that the period of oscillation of granula sharply increases with the decrease of the ratio of density between two kinds of particles. The relations of the ratio of density to the ratio of vertical height of the two kinds of particles are calculated, which shows that the main factor of granular oscillation is not the “Brazil nut effect” or “reverse Brazile nut effect”. The granular temperature is calculated and found to be relevant to oscillations of mixture. When the temperature of the small particle is above a certain value, oscillations of granular mixture occur. According to hydromechanical equations proposed by Viridi et al., these equations are correspondly modified and may explain the relations between the period of oscillation and the ratio of granular density.