Abstract: The subcritical assembly is safe, simple and easy to operate, and can be used to complete many physical experiments. It is suitable for education, training and experiment research, with its characteristics being different from those of a critical assembly. According to contract for design and construction of subcritical assembly, Jordan subcritical assembly (JSA) physics design was made to determine main physical parameters, such as optimal fuel rod size, optimal moderation lattice, optimal loading pattern, etc. The accomplished experimental results in the Jordan University of Science and Technology show that the physics design results and the actual situation of the assembly are in good agreement.