A computer booting method is provided for a computer system. The method comprises performing a power-on-self test. When the test result shows no error on the BIOS, a booting procedure is executed. When the test result shows the BIOS is damaged, whether the computer system stores a backup file of the BIOS is determined. When the computer system stores the backup file, the central processing unit reads the data of backup file and write it into a BIOS system memory and a reboot process is performed. When there is no backup file in the computer system, the computer system is connected to an internet server and downloads a BIOS backup file to the system main memory from the internet server. The central processing unit reads the BIOS backup file and write it into the BIOS system memory and a reboot process is formed.