In order to improve the reliability of remote calibration system, a task-constraint-based access control model named TCBAC is presented according to the characteristic of remote calibration system. TCBAC conducts access control according to task. It defines authorization constraints and execution constraints by the characteristics of task and the relation among tasks. Users can obtain a task authorization only when the authorization constraint is satisfied, and can execute a task only when the execution constraint is satisfied. The performance of TCBAC is analyzed by applying it to a remote calibration system and comparing it with DAC, MAC and RBAC which are commonly used access control models at present. The results show that TCBAC has the advantages of considering context and dynamics, it more fully satisfies the principle of least privilege and the principle of separation of duty and has good expansibility.