A security authentication method is provided. In a step (a), a to-be-recognized image information and a to-be-recognized voice information about a user are provided. Then, a step (b) is performed to identify and judge whether the to-be-recognized image information and the to-be-recognized voice information comply with a registered image information and a registered voice information, respectively. In a step (c), if the judging condition of the step (b) is satisfied, a security information prompt signal is generated. In a step (d), a to-be-recognized security information is provided by the user. Then, a step (e) is performed to identify and judge whether the to-be-recognized security information complies with an abnormal warning information. In a step (f), if the judging condition of the step (e) is satisfied, an abnormal state warning and processing process is performed.