High quality of security and guaranteed real-time requirements are two key goals of mission- critical embedded storage systems. But most existing real-time disk scheduling algorithms do not consider improving security performance of disk requests. A security-aware periodic-write (SAPW) scheduling algorithm is proposed to judiciously select appropriate security level for each disk request to maximize security value of N periodic disk users, while without sacrificing timing constraint of each user. Simulation results show the significant effectiveness of SAPW algorithm, and the average security improve- ment is up to 223.6% over other three algorithms.