A geometric model and mathematical model of planetary gear mechanism with double circular-arc teeth is determined using the imaginary rack cutters and double envelope concept. The mathematical model of a ring gear with double circular-arc teeth in a second envelope has been developed. In this paper, the conditions of the gear meshing and contact load of the gears are simulated by assembly errors. The goal of the stress analysis is to determine the contact stress on the planet gear and ring gear, and planet gear and sun gear. Given the assembly errors of the planetary gear mechanism including center distance error and mis-aligmment error, the maximum von-Mises stress in the planetary gear mechanism with double circular-arc teeth is analyzed using visualNastran desktop package. It is found that the center distance error is more critical to mis-alignment error.