The stretch of paper in the process of soaking and drying is an important index that affects the performance of paper used for ancient book restoration. In order to reduce the stretch rate of newly-made restoration paper, six kinds of restoration paper samples were treated with the hygrothermally-accelerated aging method, and the influence of the aging process on paper stretch was determined and analyzed. The results show that the hygrothermal aging can significantly reduce the stretch of paper, especially the lateral expansion rate and dry shrinkage rate. A short period of hygrothermal aging can reduce the stretch rate of newly-made restoration paper to a level close to that of old paper.