The capabilities trusted computing provides have the potential to radically improve the security and robustness of present systems. By combining present models for trusted computing with the thought of code authorization, we put forward a code authorization based Operation System model for Trusted Computing. This model solves the foundation security problems in the primitive model by creating a trusted chain from a core root of trust to all the Virtual Security Units (VSUs). The Trusted Platform Module (TPM) provides various security services, such as integrity checking and sealed storage, for all the VSUs and Authorization Describing Tables (ADTs). Moreover, the robustness of standard part in NGSCB is enforced for the security protection from the code authorization. This idea of code authorization can also be applied to most of present models that adopt the idea of box partition for trusted computing and improve their security to some extent.