ABS(Acrylonitrile-Butadiene-Styrene) polymer that is mainly used in home appliances are viscoelastic materials which are subject to permanent deformation when exposed to certain temperatures and humidity levels for long periods of time. In the present study, this phenomenon was defined as a creep phenomenon of Polymeric materials resulting from temperatures and humidity and a material model that can predict mechanical properties of ABS and creep behavior was selected. To establish a numerical model that can simulate creep behaviors, tensile tests to which temperatures were given and creep tests to which temperatures/humidity/loads were given were conducted. Thereafter, to consider the effect of distributed humidity inside the ABS specimen, diffusivity that can make the simulated creep behavior coincided with reality were derived from the test which is under unbalanced-diffusion condition. In particular, interpolation functions that can predict material constants that show the creep properties of ABS were derived according to temperatures and humidity levels with mechanical properties and diffusivity. Creep tests to which temperatures and humidity changing over time were given were conducted on random specimens and the test results were compared to numerical analysis results. According to the results, the results of calculations using the creep constant prediction interpolation functions and the numerical model established through the present study could well simulate actual creep behavior resulting from temperatures and humidity. Keywords: Moisture Diffusion, ABS(Acrylonitrile-Butadiene-Styrene), Two-layer viscoelastic-plastic model, Polymer creep behavior, Thermal and humidity creep.