A method of switching between multiple operating systems of a computer system includes the following steps. Firstly, the computer system is in an environment of a first operating system. Then, a system management interrupt is triggered to allow the computer system to enter a system management mode, and a controlling authority of the computer system is transferred from the first operating system to a basic input output system. Then, a backup of a first environmental parameter of the first operating system is created. If the second environmental parameter is not included in the computer system, a second operating system is loaded in a normal mode. On the other hand, if the second environmental parameter is included in the computer system, the second operating system is booted according to the second environmental parameter.