Abstract: Uranium trioxide is the product of spent fuel reprocessing plants, which can be used to prepare uranyl nitrate solutions required for plant start-up, uranium tail-end commissioning, and preparation of U（Ⅳ）. In order to clarify the optimal process conditions for the preparation of uranyl nitrate solution by dissolving uranium trioxide powder, to improve the level of uranium trioxide dissolution process in a targeted manner, and to explore its dissolution characteristics, it is necessary to study the effect of process conditions on the dissolution process of uranium trioxide. In this paper, the process of dissolving uranium trioxide powder by nitric acid under different stirring speed, temperature and initial acidity conditions were studied, the influence of reaction conditions on the dissolution process was analyzed, and the optimal process conditions were gotten. The results show that increasing the reaction temperature and initial acidity is beneficial to the dissolution of uranium trioxide. With the increase of the stirring speed, the dissolution time first decreases and then increases.