Animal silks offer the combined advantages of high strength, high elastic modulus, and large extensibility and are often used as a powerful example of the biological material design paradigm to guide synthetic polymer designs. Although much is known about quasistatic mechanical properties of animal silks, their behavior under dynamic loading conditions has not been extensively explored. In this study, we used continuous dynamic analysis (CDA), which combines dynamic mechanical analysis and the quasistatic tensile test to quantitatively measure the viscoelastic properties of silk as a continuous function of strain. CDA observations indicate that instead of the simple linear-elastic response detected in quasistatic tensile measurements, a different structure-mechanic response occurs before the yield point. Furthermore, a structure-mechanic model based on viscoelastic theory was established to understand the contribution of secondary structures to the continuous dynamic mechanical behavior of silk. The secondary structures of silks and polymers are highly similar; therefore, the structure-property relationship uncovered in this study can directly guide the design of high-performance polymers, in particular, polymer fibers with desired dynamic mechanical characteristics.