为了表征改性双基推进剂的力学行为，推导出改性双基推进剂粘弹-粘塑性本构模型。为获得模型参数，利用一系列蠕变-回复试验，将材料的总应变分离为粘弹性应变和粘塑性应变，使用最小二乘法获得了粘弹性参数，使用Nelder-Mead单纯形优化算法，结合后向Euler数值方法获得了粘塑性参数。通过不同应力水平和不同加载时间的蠕变-回复试验对模型进行了验证，结果表明，在应力水平较低或加载时间较短的情况下，模型预测与试验值变化趋势基本一致，模型获得的粘弹性应变与粘塑性应变在总应变中所占的比例与试验吻合。改性双基推进剂粘弹-粘塑性本构模型能够在一定范围内描述材料的力学性能。

In order to characterized mechanical properties of modified double base propellant, a viscoelastic-viscoplastic constitutive model for modified double base propellant is derived. A serious of creep-recovery tests are done to obtain model parameters, the total strain of material is separated into viscoelastic strain and viscoplastic strain, the least square method is used to get viscoelastic parameters, while Nelder-Mead simplex optimization algorithm combining with backword Euler method are used to get viscoplastic parameters. A serious of creep-recovery tests under different stress levels and different loading times are done to verify the model, the results show that the change trend is consistent between model prediction and test value under lower stress levels or shorter loading time，the percentage of viscoelastic strain and viscoplastic strain in total strain obtained from model agree with test. Viscoelastic-viscoplastic constitutive model for modified double base propellant can describe the mechanical properties of the material within limits.