Effect of specimen size on the residual stress distribution of Al2O3/Nb joint is studied using numerical analysis. It can be concluded that the difference of specimen size can greatly influence the stress distribution. When the height of the specimen increased, the residual stress did not change evidently, and the residual would not change any more with the height increased to some degree with the width of specimen increasing, the residual stress increased firstly. But when the width reached 25 mm, the residual stress decreased instead. In conclusion, increasing specimen size is beneficial to both residual stress decrease and structure design in practice.