Because of the light weight properties, formability and cost saving, plastics are essential materials for industrial products. In the automotive industry, many plastic parts are substituted for metal parts. Particularly in crash analysis of vehicle structure, capturing material failure is becoming important. This paper shows some issues in traditional material modeling and approach to enhance accuracy of crash analysis for unfilled plastics and fiber-reinforced plastics. The approach for unfilled plastics taking a new constitutive equation that takes unique properties of plastic into account. For the fiber-reinforced plastics, manufacturing process is considered to describe more accurate anisotropic material properties.