The statistical mechanics of an ideal polymer chain entangled with static topological constraints is studied using a superspace approach,in which the probability distribution of the polymer is obtained as solutions of the Fokker-Planck equation in a superspace with an inner structure characterized by the n-generator free group.The theory predicts that the force-extension curve of the polymer under the topological constraints has the generic form F=kI+Z/I,where I is an effective extension.Aside from the elastic term that is linear in I,the force-extension curve contains a universal term of the form Z/I.The magnitude of this topological term is determined by the topological charge number Z,which characterizes the topological nature of the static constraints.The theoretical results are further verified by a scaling analysis based on a blob model of the chain conformations.