Abstract: Study of thermal, force and nuclear radiation of weapons-grade-plutonium (WgPu) is one of the essential problems faced in the research of whole-device-storage (WDS) of nuclear weapons. The rule of decay heating power of WgPu per kilogram was obtained according to the public data, and regression analysis was implemented by the least square method because of the outstanding linear property, and thus a formula about the heating power and time was given. This equation has high precision, and could be used in the thermal dynamics study of WgPu in WDS.