International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Wireless information transmission is easy to be suffered from various threats in an open environment. In this paper, we proposed a new type of software oriented secure system for direct wireless information transmission. We first present the special functions and requirements, which have to be satisfied during introducing the secure system. Then, we divide the secure system into three stages: normal operating stage, key presetting stage, and key replanting stage. The security, reliability and the computing complexity of this system are analyzed in this paper. Finally, we carried out this secure system by software and proved the availability.