Shape memory polymer (SNIP), which has attracted lots of attentions recently, is a kind of smart material. The thermally induced SMPs can remember two different shapes because of the combined functions of polymer's molecular architecture, morphology and the specific multi-step processing technology named shape memory creation programming. This paper aims to analyze Polyurethane's shape memory properties based on the viscoelastic theory. First, the Polyurethane's creep and relaxation performances are simulated using Maxwell-Weichert model. The simulated results of relaxation process are found in good agreement with the experimental results. Later, same model is used to describe Polyurethane's shape memory effects in strain-controlled situation. As the results show, Polyurethane's shape recovery ratios are almost 100%, whereas shape fixing properties are relatively poor. Moreover, as shown by the simulated results of recovery time under different recovery temperatures, recovery time shortens along with the increase of recovery temperature.