The relaxation equation of nonwoven fabric is derived by applying the network theory with the assumptions. Relaxation phenomenon anticipated from the theoretical relaxation equation is compared with experimental results by using random-laid nonwoven fabrics. The experimental results of initial stress part coincide well with the theoretical at small strains while deviate significantly at large strains and the initial stresses relax slowly and steadily in actual case than in theory. The difference between the theory and the experimental can be explained through the plausibilities of assumptions.