Abstract: Northwest Rockii tree peony cultivar group is one of the major tree peony cultivar groups in China.We describe an outstanding Rockii tree peony cultivar named ‘Spring in Arm’(Paeonia rockii ‘Wan Chun’,‘Wan Chun’ in Chinese pinyin or pronunciation) which could be regarded as a representative among the in-group cultivars in aspects of the characteristics and performance.The Rockii tree peony cultivar plants are suitable for ornamental uses,economic plantations,afforesting barren hill and mountain districts or desert control.According to long-term investigations and related literatures,the regions in China where Rockii tree peony cultivars are possible to be introduced into,are attempted to classify into four categories,based on the degrees of introduction and cultivation difficulty as well as adaptability.Key techniques and measures to be paid attention to necessarily in the aspect of transplantation and cultivation have been described briefly for each category of the regions.Discussions have been conducted on the problems in the nationwide releases of the Rockii tree peony cultivars in China,and suggestions for the solution have been put forward.