The traditional border access control based on the users` identities has not yet satisfied current security requirements of access control. Trusted Network Connect (TNC) makes the admission decision of an endpoint to a network by performing integrity checking, which effectively solves the problem of network access control. However, the TNC architecture has not referred to the content of system access control. Because system access control plays an important role in perfecting the whole access control mechanism, it is valuable to research the system usage authorization in trusted platform. To solve the problem, we propose a usage authorization model with time constraint based on TNC named UAMTC by combining with Usage Control (UCON) which is the next generation model of access control. In UAMTC, we design three important authorization mechanisms to implement abundant policy decision factors and continuity of decisions. These mechanisms are assignment of roles and permissions, security degree and time constraint. The simulation experiment results show UAMTC can effectively solve the problem of system usage authorization in the TNC environment, and provide better security and availability.