To predict the optimized planetary gear sets that have quite gear noise in early design stage, Planetary Run Many Cases(here after pRMC) program which is using the combination analysis method of all gear specifications to find out the best planetary gear specification is developed. The pRMC is composed of 5 steps, generate, setting, evaluate, combine and analysis and been also capable of analyzing any number of simple, compound or complex-compound planetary gear set. After calculating of all candidate gear sets, pRMC could show some results likewise transmission errors, sum of forces, contact ratios and so on. By using the pRMC, the best planetary gear sets which have low noise level could be developed easily and successfully in the new automatic transmissions and others.