T-400 is an elastic fiber developed by Dupont. It was commended as one of the best developing prospect chemical fiber in the 21 century. In this paper, the elasticity of spun silk/T-400 interlaced fabric was studied. The elastic characteristic of the spun silk/T-400 interlaced fabric with different warp density, weft density, fabric intensity and fabric weave were tested and analyzed. And the stress relaxation was studied. It shows that elastic reversion at certain elongation of the fabric is correlative directly with the warp density, weft density, intensity and weave. The elastic reversion at certain elongation decreased following the warp density and weft density increased. And it was increased following the ratio of weft intensity to warping intensity and the fabric average float increased. The time of stress relaxation is longer if the warp density is larger. The time is shorter when the warp density and the fabric average float is larger. And the correlative curve was pictured and the correlative formula was built.