Calculation of robot's reliability life is useful to predict the time of replacement of robot part in order to improve continuity of works. To obtain its tendency of failure, Wiebull Distribution is employed, which contain the characteristics of failure. Accelerated life calculation should be employed to reduce the time of reliability test as it reflects the rate of torque and revolution. It is suggested that the method of how to calculate accelerated life using formula of life test for bearing and how to predict failure tendency of harmonic reduction of robot arm using Weibull Distribution. Also, this paper shows that needed motor power and suitable Accelerated Factor(AF) can be calculated using Accelerated Life Test.