1. A computing system provides normal security services and high security services with a single operating system, comprising: a secure application programming interface (secure API) for the high security services, called by a pseudo normal thread executed while the computing system is in a normal security environment; a driver layer invoked by the secure API, calling a world switch instruction; a monitor, activated by the world switch instruction from the driver layer to save context of the pseudo normal thread, change the computing system to a high security environment, obtain a secure thread corresponding to the pseudo normal thread, create or restore context of the secure thread, and dispatch the secure thread to be executed by the computing system that has been changed to the high security environment, wherein, the secure thread relates to one of the high security services.